G'day, Starting today my computer has been randomly turning itself off, although running lights are still on, and the computer sounds as if it is still running normally. Essentially what happens is that it crashes out, the monitor says input signal lost and then nothing happens. First two times it crashed whilst using Photoshop. Third time I installed a program to monitor the HDD temp. It was running just over 40c when it crashed again (had a low end game running to see if the HDD temp would rise). I waited 30 min before turning the computer on each time. Opened the case to check for any build up of dust, it seemed fine. Edit: I have also checked that all the cables are plugged in correctly. Also definitely something wrong, because one of the times holding down the power button didn't turn it off. Had to turn the computer off by the switch at the back of the computer. The other times it went to BIOS then turned off. System: Windows 7 64 4 GB RAM 2.8GHz Quad core 500GB Seagate HDD Only thing new with the comp today was updating Microsoft.Net framework, a few hours before the first time it crashed. No idea if that is related or not. Thanks for all help in advance, Sam.