I have a friend's 64 bit Win 7 Compaq desktop machine here. It was running slowly and full of junk and malware, so he had the OS restored to day 1 condition at the local PC store, and then I took it over to install his programs. Oh, and all the Windows updates since Day 1, something the PC store didn't bother with. The few programs I have installed work just fine, and everything I have tried within Windows 7 works OK.
But there is one major problem which is that sometimes it just will not start up - all I get when I push the power switch is a blank screen with a cursor flashing about once a second in the top left corner. The only way out seems to be to press the on-off switch again - sometimes several times - or just disconnect the power, as there is no response to the mouse or keyboard. Other times, it starts perfectly normally. There is no pattern that I can see to this. Logic tells me that if there is something wrong with the software controlling the start-up sequence, it would fail to start every time, whereas if there is an intermittent hardware fault that could be the cause. I have run chkdsk a couple of times with no result. I have been messing about with PCs since DOS days and haven't had an inconsistent problem like this before, so can someone point me in the right direction please ?