Hello.
 
I'm asking for help after 4 days of fighting with my PC. I was on every forum Google can find and I still don't have any clues. I replaced some of my hardware and my problem is still there. I'm out of ideas. But let's get to the point.
 
My PC is about half year old and I never had any problems with it. Recently I'm getting random BSOD. It's happening when I play games or working in Windows XP SP2 (but rarely). After BSOD my monitor is giving me "No Signal" message. When I manually reset or turn off/on my PC nothng changes. I still have "No Message", but I hear Windows starting in background. Unplugging and plugging back my LCD screen doesn't help. Changing DVI ports doesn't help aswell. I have no idea what to do.  
 
First I thought it's graphic card going crazy so I bought new GeForce (specs below) and plug it in. At second powerup this new card stop working for me and I'm getting error sound message from BIOS (1long, 3short beeps). After that I thought it's motherboard after all. So I bought new one (spec below), but nothing has changed. My Geforce doesn't work, my ATi is causing random BSOD's. But I have to admit that for 2 days everything was fine.  
 
I was experimenting with memory modules (removing all from motherboard and leaving only 1, etc), but doesn't help. I removed dust from everything I could. I checked processor and put new compound on it. Still without any results. I was checking temperatures and I got reports from 35-70 degrees (dependable how long system is working). I have an extra 120mm case fan. Everything is working fine, fans are running fast without any noises.  
 
I was checking every Catalyst drivers possible. Startting from 8.3 to 7.6. I applied HDMI fix for them. I'm working on 1280x1024 resolution and I was changing refresh rate to 60 to 75MHz. It' still there.
 
Do you have any ideas what can it be? Because it's becomming very annoying at this point.
 
My PC spec is:  
Motherboard: Asus M2N-E SLI / Winfast MCP61SM2MA
Processor: AMD Athlon 64 X2 Dual 5200+
Graphic card: HiS ATi Radeon HD2900XT 512MB / XFX GeForce 8500GT
Memory: A-Data 4GB Dual DDR2
LCD Screen: AMW 19" X1900DS  
Power Supply: Tagan TG580-U15
 
Thanks for any ideas. Kind regards, Greg

Since you replaced the mobo,graphics cards and did the obvious memory test.
I would have to say that your power supply is probably crapping out on you.
Have you tried a newer supply? How old is this Tagan psu?

I blame everything that happens on AMD's.  I NEVER had issues with any intel system I've created.  I get calls and have issues on my own with AMD systems.  Be it the board, the chip, the ps utilization - whatever the reason, I think AMD cuts corners and just plain sucks.  
 
Probably what the other posted above - power supply.  But for me, AMD is always somethign I look at as being the problem.  
 
They are teh volkswagen of the computer world.