With the home version of windows being $109 and the Pro version being $199 its not economical to upgrade a vacuum tube computer to windows 7 or 8 or 10 when you can get a newer 240% faster machine WITH 2 gigs of ram AND windows 7 for $99.  The windows 7 alone will be more than that.

http://www.walmart.com/ip/Dell-Refurbished-OptiPlex-755-Small-Form-Factor-Desktop-PC-with-Intel-Core-2-Duo-Processor-2GB-Memory-160GB-Hard-Drive-and-Windows-7-Home-Premium/20565348

I wouldn't mind buying a cheap video card and a CPU to upgrade this old workhorse

Install a new micro-ATX motherboard and memory.

That right there is an excellent buy. However if I were looking at cheap and small, I would rather do a Winbook tablet (like my TW-700) connected to my existing desktop monitor for $70, which includes windows 8 and a year of microsoft office 365.

What I'm trying to do, however, is to max out, not my post count (as others try to do), but the specs of my old Dell laptop. I know I can do it for less than $40. Like I said, I upgraded the CPU and RAM on my 5150. It cost $10 shipped for the RAM and $6 shipped for the CPU and thermal paste. I just need to know what parts to buy on eBay for my Dimension 2400. 

Like I said, I upgraded the CPU and RAM on my 5150. It cost $10 shipped for the RAM and $6 shipped for the CPU and thermal paste. I just need to know what parts to buy on eBay for my Dimension 2400.

Unlike the 5150, it employs an architecture bordering on obsolescence even when new.

There is no cheap way of substantially boosting performance. A faster processor isn't that much help, considering that the video and storage are both major bottlenecks.

BIOS  A07   0HJ054 LGA 775 Socket T  DDR2 motherboard version of the E510/5150 motherboard works fine with Pentium D Pressler 900 series from 915 to 945.  It supports 3.25 gigs of ram and windows 7,8,10. It has a PCI-E X16 video slot and 305W power supply.  The 2400 has none of these features and never will.

E510 does not support Core2 duo. 

The Pressler vs Smithfield can do LAHF and SAHF as well as CMPExchange16 which means it works fine if you have a 900 series Pentium D.  That means you can run 64 bit windows 7 or 8 or 10 just fine.  Max useable ram will always be 3.25 gigs regardless of cpu or os being 64 bit or not.  This is a chipset limit.

The 5150/E510 can do this(with caveats like Bios A07 and the Copper Heatpipe Heatsink Exactly the same as the GX620. Motherboard Version 0HJ054 supports the Pentium D without issues up to 945..E510  from Oct 06. The Pentium D 915 is the universal CPU which works in Tower or even low profile or SFF or USFF when it has the copper performance heatsink.

Description	Supported OS	Download
Dell Dimension System BIOS, A07 Dell DM051 A07 System BIOSMore details	BIOS

On older GX320,330, 360, 520,620,745,755,760,780 and Precision 380 or T3400 a bios update may be required for Pentium D 900 series to work.  An additional problem is that Early 5150 models need Bios A07 and they will stop on Unsupported processor Press F1 to continue. This is only older boards.  Other than having to press F1 it works fine.  I'm running 64 bit windows 10 on one right now. The crossover machines were the Mr Smith Mini Tower GX280's  They look just like the GX620 but the board in them is older and there is no Pentium D support.         

Description	Supported OS	Download
SIGMATEL STAC 92XX C-Major HD Audio, v.6.10.0.5343, A02 Sigmatel STAC92XX C-Major HD Audio DriverMore details	Windows Vista 32-bit Windows Vista 64-bit
SIGMATEL STAC 92XX C-Major HD Audio, v.5.10.0.4823, A05 Sigmatel STAC92XX C-Major HD Audio DriverMore details	Windows XP Windows 2000 Windows XP x64

I got my 8.1 pro upgrade back when it was $38.  If they want that they should buy it immediately because there will not be any in the future.

WINDOWS 8.0 is depricated and the Purple box 8.1 home and Blue Box 8.1 pro are the available everywhere retail options.

After Oct 31 2015 8.x may be gone forever as well being replaced by Windows 10.

Pentium D 915's are very cheap as is the copper heatsink.  The ram and windows license are the expensive parts.  You update the bios to latest then change the CPU and replace the thermal paste.  The Dual core pentium D is an improvement. 

http://www.ebay.com/sch/i.html?_nkw=pentium%20d%20915

http://www.ebay.com/itm/Precision-380-390-T3400-XPS-400-CPU-Cool-Copper-Processor-Heatsink-Shroud-X9694-/131310107549

About a year ago, I upgraded our Dimension 2400 with a new motherboard, CPU, RAM, and Power Supply. I already had some of the parts so it wasn't too expensive - these are the parts that I installed:

• Gigabyte GA-78LMT-USB3 Motherboard
• AMD Athlon II 260 (cheap / used from eBay)
• 16 GB Corsair DDR3-1333 RAM
• Antec 400W NeoEco Power supply (already had it)
• 2 SATA DVD burners
• 1TB SATA WD Blue harddrive (already had it)

I loved the size of the case and that it doesn't scream "expensive" (steal me!). I really wanted a brand new PC with the old Dell case. All of these parts all fit nicely into this case - the only challenge was the power button / LED indicators as they had a proprietary connector that went to the old Dell Motherboard. After a lot of searching and thinking about just splicing the existing wiring to standard connectors, I found a StarTech harness replacement kit (StarTech BEZELWRKIT) for about $6:

www.newegg.com/.../Product.aspx

The power and reset buttons fit the original Dell bezel perfectly. It didn't match the LED size perfectly, but I was able to get the bigger LEDs to fit into the plastic holders with careful force. Now I have an "old" Dell 2400 with brand new internals - tons of HD and RAM - and best of all - Windows 7. It runs many times faster, never crashes, and it sleeps when I'm not using it (the old OS / Motherboard ran 24/7) saving power and not filling with dust. I haven't had any problems with it since and it seems to run cool.

The photo below is midway through the upgrade. I also added an Antec 92mm SmartCool temperature controlled fan to the back of the case using the existing holes. All-in-all, this case is very upgradable. The only thing that I couldn't connect was the case USB on the front - I use a USB3.0 port on the back connected via cable to a 4 port USB3.0 hub on my desktop which is more convenient anyway. 

The switches fit perfectly - that was the part I was worried about and I really wanted new switches anyway.

As I remember the Dell case had a mix of small and standard LED indicators - the StarTech kit had all standard LED indicators. The standard LEDs fit and for replacing the small LED, the plastic clip that holds the LED was just "stretched" a little and the standard LED slipped in without cutting / changing anything on the bezel. I certainly could have spliced in a small LED and done new heatshrink tubing at the solder points but there was no need - it worked well.

I am ready to try the GA78 ...they are avail from G/B at about  $36.00 and up. I already own the same Athlon II and a Xion 450w  atx psu,  some ram, etc. Can you please advise me on other concerns I may face with this. Will the 2 existing case fans plug into the board and what about the rear I/O  shield (I hope it comes w/ the new board) ...any mods required?  Ist time build/builder. Thanks,  dell380.