I'm getting infrequent but regular crashes - about once a week, usually when the machine is left unattended. The screen shows exactly what it would if all were working correctly, but the system is frozen. No mouse or keyboard actions do anything. There is nothing in the Event Viewer log to indicate what happened. The only cure is to power down and restart. There is one indication that may be meaningful. The PC has a "hard drive activity light" which flashes when the drives are in use, and about once every few seconds anyway. That light is permanently "off" when the fault occurs. I've tried the mechanical optiions - checked all chips and cards are seated, replaced SATA cables with high-quality locking ones, etc - which made no difference whatever. It's Windows 7, 64 bit, Pentium Quad Core, Nvidia GeForce GT240 graphics card, 2 SATA hard drives and a CDROM drive, various USB peripherals. I've tried with no USB apart from mouse and keyboard - no difference. Can anyone suggest actions to try? Google and Searching finds no cases with the "normal screen but locked" (or, shall we say, I can't find any). Keith

An additional bit of information: The PC did it again this evening. I noticed that the disk drive activity light flashed immediately before the crash. Again, there is nothing in the Event Log. However, when it restarted, it took a bit longer than usual to find the first hard drive, and when it listed the hard drives as it was booting, the name of the first drive was gibberish. Normally, it would give maker's name and model number. Once it had booted, all seemed well and the Control Panel gave the right drive model name and number etc.KeithjUK

Hi, According to your description, I suggest you to upgrade the driver of Hard Drive and SATA controller for a test. Also, you may try to boot the computer in Safe Mode to determine whether the 3rd party software cause this issue.Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Three months later, I finally found the cause. The graphics card was faulty, and would briefly draw more current than the power supply was capable of. The card would resume operation, but the CPU had crashed by then. A new graphics card, with a separate power flylead to it (so not powered solely by the slot) has fixed it.KeithjUK