Dell 4700 Motherboard woes

The light patterns indicate a memory or motherboard issue. Based on the bubbled capacitor it sounds like you should replace the motherboard if replacing the capacitor is not an option and even then there could be other problems and issues caused from this. It's probally best just to replace.

Below is the spec's of the motherboard you would want for that model. 

Manufacturer: Intel (OEM for Dell)
Dell Part#: M3918 DH682 Dimension 4700
Chipset: Intel D915 D915GOK 915G Express
Socket: LGA775
Front Side Bus Speed: 800Mhz FSB
Supported CPUs: Intel Pentium 4 processor 520, 530, 540, 550, 560, or 570 with HT Technology - Intel P4 that runs at 2.8, 3.0, 3.2, 3.4, 3.6, and 3.8 GHz
Other Features: Hyper-Threading Technology Support
Supported Memory: 400-MHz (PC-3200) and 533-MHz (PC-4300) DDR2 unbuffered SDRAM non-ECC
Maximum Memory: Support for up to 4 GB of memory
Video: Integrated and PCI Express 1X and 16X
Sound: Five connectors for line-in, line-out, microphone, surround, and center/Low Frequency Effects (LFE) channel; one front-panel connector for headphones
Expansion Slots: 2 PCI
Connectors: PS/2 Mouse, PS/2 Keyboard, Printer Port, (6) USB 2.0 Ports, 1 Serial Port, 10/100 Network LAN
Peripheral Interface: Two Serial ATA (SATA) Interface
Other: Two IDE Channels Supporting ATA-66/100/133 IDE, One Floppy Controller

If it's the motherboard (and it sounds like it), only another Dell 4700 motherboard will work without major issues.  Dell uses a Proprietary and Undocumented front panel connector so putting a non-Dell motherboard in will present problems trying to connect to the front panel power switch and other jacks.  Second, if a non-Dell motherboard is used you will need a new copy of Windows as the Dell will only install on a Dell motherboard. 

There are companies on the web that sell used/refurbished Dell motherboards.  That is probably the least expensive way to get it working.  Considering a used 4700 PC is not work more than $50 and maybe $75 at most don't put much $$ in it. That may sound bad but it's reality.

You can get a Dell OEM motherboard for the 4700 here for $80 with free shipping.

Only you can determine if it's work the the money vs getting a new system.

Ron

Another thought:

Did you pull all the RAM modules, except the one in slot 1 and see if it boots that way? Then swap all RAM modules into slot 1 to see if one of them is bad?

Ron

Newegg has a $50 special on a brand new P4 mainboard with which the 4700 parts should be compatible with. The power supply will fit in a good quality generic case like the Cooler Master offerings. 

As for Windows, you can run a repair install and then call Microsoft for an activation code. Tell them the truth, which is that the mainboard died, and they will give you a new code. Been there, done that. 

Keep in mind that Dell uses a proprietary connector between the front panel and their motherboards. The pin-outs for that connector are  unfortunately not docuemented anywhere.

So if you go with a non-Dell motherboard, you'll also need a new case.

Good luck, whichever way you go.

Ron