Hi im having a few issues with my PC and could do with any ideas.

System Specs
Athlon 64 3400+ Newcastle - Processor
ECS rs482-m754 - Motherboard
600w - PSU
1gb Corsair XMS PC3200 DDR - Ram
Radeon X1900XTX - GPU
Maxtor 160gb - HDD

I have assembled this PC and been using it without major issues but just lately i kept having a few issues with overheating and it kept causing the PC to crash so i opened it up and began to de-dust the machine. I do this quite regularly. I touched the inside of the PC to get rid of any unwanted static, i then took out the case fan, the processor fan, the GPU and cleaned them. I then noticed the ram was a bit dirty so i cleaned it also. I then found some old 512MB ram from an old PC and decided i would try and slot it in with the corsair XMS and see wether it would throw any issues at me. BIG MISTAKE!!. I assembled the PC back together and checked every possible fitment is in the right place and correctly connected. I then booted up the PC, and i could smell a musty burning smell, the last time i smelt this type of smell was when i burnt out my old PSU. I immediatley switched off the PC opened it up and investigated. There is no sign of any burn damage on the motherboard, on the ram sockets, around the GPU or the PSU. So thinking it must of been that 512MB ram stick that has caused it i looked at that and the module had no damage either. I then left out the 512MB ram stick and tried booting the PC with just the Corsair ram, and found out that the PC will no longer send any kind of output to the monitor, and all im getting is 'NO SIGNAL' from the monitor. The PC itself will fire up, all the fans spin, the GPU gets power, and all my LEDS. I have tried trouble shooting this for 8 hours and now im at breaking point. Things ive tried include:-

Resetting the CMOS jumper
Disconecting all RAM then boot
Disconecting the GPU then boot
Disconecting the LEDS then boot
Disconecting the on board audio then boot
Disconecting the Corsair RAM and using the 512MB RAM then boot
Disconecting the CPU, clean de-dust, and reapplied new thermal grease.

I was going to try disconecting the DVD Drive and the HDD but i just cant see the issue relate to either of these components.
The only thing i have noticed is that the Corsair XMS RAM which is the model with LEDS on it, used to light up all the way along the top with all 9 LEDS showing colours, RED, ORANGE & GREEN. Now it only lights the middle LED which is orange. I am wondering wether it has burnt outor if the system is in some kind of safe mode. I have tried the 512MB RAM stick in the machine without the Corsair stick and it still throws up the same issue, 'no signal'. I am aware that you are not supposed to mix different memory modules but didnt think it would cause an issue like this. I suppose its possible that both the ram sticks are fried but there is no exterior damage to either.
I have tried smelling all parts of the PC to see where the smell originated from but to no avail. My motherboard does have an on board graphics (RADEON Xpress 200) but i cannot try to switch from the x1900 GPU, back to the Xpress 200 GPU as i have to do this via BIOS which i cannot see as there is no display so cannot eliminate the x1900 GPU from the troubleshoot. I have tried everything that it could possibly be, and am now wondering wether one of the components has failed but it all seems to be getting power, it just wont send the signal to the monitor. This PC has worked generally without fault for 2 years and never had this issue and as i took care removing the components, it must be the RAM. Has anyone out there had a similar issue?? Is there anyone out there who can help?? All responses are much appreciated because as of today my PC is little more than a paperweight.

It sounds to me like you're motherboard needs replacing. Otherwise your monitor is the problem.

The easiest way to find out would be to hook the monitor up to another pc. If it works then I'd look at replacing the motherboard.

Unfortunately with no display it's hard to do troubleshooting. So test the monitor first.

Thanks for reply. Ive tried the monitor with another PC and it works fine and had the motherboard out to check for burn damage there is none. Again i have noticed that the Corsair RAM will only light up the middle LED, making me wonder wether the RAM slot on the board has gone. Im at a loss as to wether i buy some replacement RAM modules and try it or if this would be a waste of money if the RAM slots are the problem. So do you reckon a new motherboard is the way to go or new RAM modules.