Computer freeze - and then black screen after restart

Hello ,
for the last 4 days .. my computer stucks alot while playing games ..
just crazy colors appears and then my computer restart ...
at the 1st time happened , i just logged in again to windows and kept playing .
but yesterday , while playing a game .. my computer stuck and after self-restart ... it showed me black on the screen and nothing happened while my pc is turned ON.
i cant see any thing ... no Motherboard logo no nothing on start .. JUST a turned on computer with no screen .. i sent my computer to friend he changed the GFX , cpu and ram ... it didnt work .. after he tried that with no result , he put all my stuff back .. and Suddenly i got a screen ... i took the pc home and turned it on ... i succeed to login to windows vista for 1 min and then i got blue screen with " *** STOP: 0x00000050"
and then again .. no screen after restart !! i changed the screen but its the same ...
i have 2 OS , windows vista ultimate 64bit and windows xp pro..

All this problems happened while using vista .. as i remember the partition which vista installed on has 2-5gb free space ... "95% full" and mayb the driver isnt updated for the gfx .. "catalyst"

after booking the problem on the internet alot of ppl say many things .. i just cant figure it out ...
how can i slove this problem ? wt could be the problem ?
** i tried to turn on the computer without the RAM and the Hard disk .. i got no BEEP sound !! weird ?! could be the MB? GFX ?

Notice that its the 1st time i get that blue screen .. the crashes which i got befor was , either alot of crazy colors or just STUCKS , nothing moves(mouse,keyboard"num lock" .. etc "

My pc :
Asus p5q-deluxe MB
Sapphire HD4870x2 2gb
2X2gb Dominator DDR2 1066mhz
Inter Q9550 Quad core


Thanks , and sorry for bad english ...

What PSU are you using to power your rig?
What is its overall wattage and +12v amperage?
Do you have anything overclocked?

Try these and see if anything fixes it.

Clear the BIOS. Manually set the RAM speed, voltage and timings. Leave your CPU and motherboard at stock speeds.
Test the memory using Memtest.
Double check all cable/power connections.
Remove and reseat your GPU, RAM and all addin cards.
Check for dust clogging your heatsinks/PSU and clean as needed.
Check to be sure your CPU heatsink is properly attached and check the temps in the BIOS.
Test your Hd with the manufacturers utility.

Somehow i cant edit my reply .. so here another reply

My Cpu temp was around 40-60 with Thermaltake ‏TMG iA1 CPU Heatpipe Cooler‎.

My Gpu temp was around 70-90 with the orginal GPU fan " Sapphire "

thats either mem graphics or mb
what you should have done is see if it crashes under xp
but if you still cant access anything try changing the gcard to 1 u no is working
and try changing the ram
try changing to the other dvi port
if none of these works then its the board, u can test the psu also because if its not supplying power then nothing works
try a diff monitor
troubleshooting is basically a really annoying game of eliminating variables hav fun dude

I Can ALMOST Gaurantee That Is A Bad Graphics Card, My Second Educated Guess Would Be A Bad Power Supply

concern* , and why they dont fix the edit post option ?!

As Intel Specs the P45 chipset to a max operating temp of 103°c, I doubt your issue is with it overheating.
I would assume that your system would be crashing from other componets failing before your (relitavly) low power chipset hit max temps.
Most likely, you were just unlucky enough to get a lemon.
RMA the motherboard and make sure your case has adequate cooling.
Keep track of your Nb temp with something like SpeedFan and, if you see it starting to get to hot, look into adding more case cooling or a spot fan.

http://en.wikipedia.org/wiki/Retur [...] horization

Basically, you need to go Here and tell ASUS your motherboard is FUBAR.
They will then have you send in your defective motherboard and, in a few weeks, send you a new/fixed one.
Usually it is a pretty harmless procedure, just a bit of waiting involved.