Precision T1500 that keeps forgetting how much memory it has

Trial and error is the only way to test. Test one chip at a time in every slot, rebooting every time you change slots or chips. It could be one of the slots on the board is failing too. That's why you test each chip in all the slots.

Four hours on MemTest86 and no error shows up!

19 hours continuous test using MemTest86 and no error shows up!

Why don't you just do what Mary said about removing modules and trying them one at a time in all slots with reboots in between?

You could get very old waiting for MemTest86 to finish...  :emotion-4:

Besides, it might not even see a problem if all modules were recognized when you first started the tests...

Errors found after 26 hours constant use!!! Seem to original in first stick of RAM judging by the address range.

What's the color coding on the mobo for blue and black slots?

I have three sticks of 2GB @1333 MHz DDR3. However I don't think I can buy 2GB sticks anymore only 4 or 8GB.

The colors are for matching pairs. You should replace the bum module as a matched pair.

Check crucial.com for compatible RAM. This system handles 1, 2 or 4 GB modules up to a max of 16 GB. So if you buy 2 matched (whatever size) put them in slots with same color clips, and put 2 of the working originals in the other pair of matching slots. What size RAM you buy depends on budget and if you want to improve PC performance...

Assuming all 4 original RAM modules were matched, you can keep the working good one as a spare, in case any of the other originals fails. Just be sure you know which one failed and which one still works. 

Life is too short to be waiting for memtest86 to run again... :emotion-4:

Well obviously I wasn't glued to the screen while I ran MEMTest.:emotion-4:

Well I've looked up the memory for my machine and it doesn't list the cycle rate in Hz only in 1600 MT/S!!!

I want DDR3 1333MHz

uk.crucial.com/.../CT4046473

Don't know when Crucial started listing RAM in MT/s, but you can contact them to ask the speed of these modules in MHz

Even if they're 1600 MHz, RAM runs at the speed of the slowest RAM that's installed. So if you install 1600 MHz RAM along with 1333 MHz RAM, it all runs at 1333.

Gone from bad to worse with this PC!

 Ok got memory from Crucial plugged it in and it was ignored by BIOS.

 So next I thought I would take out the new memory and plug the existing memory into the slots that the new memory was plugged into. I needed to remove the video card to get better access. I reinserted the video card booted up and no video display.

 So I removed the video card and put in a spare card I had, still no video!

 No beeps from computer and no lights to indicate problem. Craptacular!

I've tried pulling the mobo battery, no effect, still no video.

I've tried using the on board video, no effect, still no video.

Are you pressing / holding power button for ~30 sec after removing the battery (with unit unplugged from wall)?

Did you try onboard video with the video card removed? Onboard video ports are typically disabled when a video card is installed.

Is the battery any good?

Can you test the monitor on a different PC or known working monitor and known working cable on this PC?

Strip it down to bare essentials. Disconnect all drives except boot hard drive, remove all RAM except the one in slot 1, remove all PCI cards except video (or use onboard video), etc. Then reset BIOS by removing the battery and pressing / holding the power button for ~30 sec. See if it boots now with only mouse, monitor and keyboard connected.

There's a note in the service manual about Integrated Video: NOTE: Intel Core i5-750/750S, Intel Core i7 860/860S/870/880 processor types do NOT support integrated video. I have a i7-870.

Tested battery at 3.03volts, replaced with newer one at 3.35volts.

Tested display, works ok on different computer.

Tried different graphics card on different display no video. LED at rear of computer show solid green, no beeps on startup, CPU and case fans spin up, along with hard drives.

Just removed all graphics cards and tried and really old PCI graphics card, still no video.

Toying with the idea of buying a PCI Express x1 graphics card to see if it's not the PCI Express x16 slot that has issues.

Does Dell still carry replacement mobos for my system?

Update:

I'll post this update for any T1500 owners out there. Managed to get the computer booting / working by putting the memory into only the two blue slots. One or both of the black slots must have issues.

I was looking into building my own system, (certainly not going drop another £800 on a Dell), however I'll persevere with this system as is.

At least you got it working, but sorry about the slot issue. Squirt some canned air into the black slots on the off chance...

You might be able to pick up a (refurbished) motherboard from one of the companies that sell OEM Dell parts...