Troubleshooting random crashes

[frh]

Hey everyone!

I built a Pc less than a year ago, and up until a month ago it was working brilliantly. However, I began getting random system hangs - these occured in two ways: firstly, the screen would go "blocky", and any sound in the back ground would repeat on a half second loop. This exclusivley happened while in a game. The second way this could occur is that the entire screen would just freeze - no evidence of a crash other than the fact the mouse was unmovable, no keys did anything and the capslock key light would not turn off or on.

1 x Sony DRU-190S 20X DVD±RW DL & DVD-RAM Serial ATA - Retail Multi Bezel & Nero
1 x Corsair 650W TX Series PSU - 120mm Fan, 80+% Efficiency, Single +12V Rail
1 x Samsung SpinPoint F1 HD103UJ 1TB Hard Drive SATAII *32MB Cache* - OEM
1 x NZXT Tempest Steel Mid Tower Case - No PSU
1 x Sapphire HD 4870 512MB GDDR5 Dual DVI HDTV Out PCI-E Graphics Card
1 x Corsair 4GB Kit (2x2GB) DDR2 800MHz/PC2-6400 XMS2 Memory Non-ECC Unbuffered CL5(5-5-5-18) DHX Technology Heat Sink Lifetime Warranty
1 x Intel Core 2 Quad Q6700 2.66GHz Socket 775 1066MHz 8MB (2x4MB(4MB per core pair)) L2 Cache OEM Processor
1 x Black Multimedia Keyboard - USB/PS2 Connection - UK Layout
1 x OCZ Vanquisher CPU Cooler For Sockets AMD 754/939/AM2, Intel LGA775
1 x Samsung Aqua SM2253LW 22" TFT Monitor 1680x1050 1000:1 300CD/M2 5ms DVI widescreen Gloss Black 3 Years Onsite Warranty
1 x ASUS P5KC AiLifestyle Series iP35 Socket 775 8 channel audio ATX Motherboard

Now, I think this is not a software problem because it occurs within both vista and windows 7 (both 64 bit). It has not occured under Ubuntu, but that might just be chance. I don't think it is anything to do with overheating - for one there is the automatic shut down which does not occur, but also I have checked temperatures, and it can occur when the graphics card is at around 67 degrees (the default idle temp of the HD4870 in my system). The CPU temperature is sub 50 degrees when these occur. I have also run memtest, which came up with no RAM errors.

I had a thought that it might be due to the graphics card - and different levels of strain causing it to crash, which would explain why Ubuntu with it's light graphics did not crash, whereas the more intensive windows did. This does not make overly much sense though, as it has been possible to play games for several hours before a crash, whereas sometimes windows will crash in minutes.

I also tried changing graphics drivers, which appeared to make a difference (the crashes became less frequent) however they did still occur and it may have simply been due to the random nature of when they occur!


Any help would be much appreciated! If it is a hardware problem, I would love to solve it before warrenty runs out!

Many thanks,

Frh

[Force Flow]

Try running memtest86 to check the RAM for issues...that's usually the best place to start

[frh]

I have run memtest86, and it shows no errors.

[Force Flow]

Do you have the latest video card drivers for Windows vista/7?