running windows 7 ultimate 64 bitthe system keeps crashing/freezing, no BSOD, nothing in the event log, just complete system freeze. sometimes it may crash several times a day, sometimes it may go for several days without crashing. Some things I have found which regularly cause a crash. Trying to print. starting a program web pages with flash or video I leave my computer on 24/8, and it even crashes at night when it is not in use. What I have tested....I ran memtest overnight, and problems with RAMI have replaced hard drivesI have tried 2 different graphics cards Have tested the PSU with a PSU tester, no issues.Unplugged all external devices other than keyboard, monitor and mousestill problem persisted.So I have done a completely clean install of windows 7 on a new disk.Still the same problem.I don't have any way to test the CPU or motherboard as possible causes.I have run windows in safe mode for several days, no crash. I have run from Ubuntu live for several days with no crash. So it does seem to be a windows issue. I cannot get a crash dump as the system is completely unresponsive, I have already followed instructions for force a crash dump via keyboard when it crashed, but this doe snot work. The few times the system has BSOD'd, it does not create a dump file or the file is 0kb, there is plenty of space on the disk, and it is setup correctly as per the M$ KB article. any suggestions.