Yesterday my computer wouldn't boot up properly anymore...

I have installed a new anti-virus (bought the CD) to it on Friday. It worked OK. When I turned the computer off I left the CD inside.

Yesterday when I switched it on - it wouldn't start. I just seemed it would try to start and get restarted every time. I checked the CD unit and saw the CD was in. After I removed it the windows started normally. It already seemed strange, but I though maybe there was somthing like a CD boot up that messed it up.

Today there was no CD in the drive (no disk either) but the same thing happened again. It was only after I hard-reset my computer that it worked and it seemed like it didn't even know it had a problem.

Unfortunately I have this habit of pushing the on button when I decide to get up (not actually use the computer - it's turned on most of the day after that), so I usually don't wait in the room until it starts running. So I didn't see what exactly happened (I'm not even sure, it gave the option to enter the BIOS setting). But I don't want to turn it off right now - as I'm not 100% sure I could turn it back on again (and I don't want to lose certain data - I'm making back-up copies now).

Does anyone know what the hell this problem could be?

Make sure that for some random reason cd booting has appeared in the boot order twice in a row before the hdd it may seem unlikely but check.

it wasnt in cd, win. if no drive is inserted which is supposed to be first to boot it goes to next boot drive without restarting..

well, my computer was working without any problems but guess what, same thing happened to me=/
after i turn off power supply (with that switch in back of the computer, i dont know how is it called in english=P) or make hard reset during some difficult process it wount just turn on and "freeze" before bios, just stay passive and hdd led lights. computer boots again after waiting a moment and then turning off and on again.

it happened on my old celeron 400 and even after i changed computer to new (whole case was changed, i didnt change monitor only), problem stayed! after hard reset computer couldnt boot.

and i still dont know what to do, is it in some bad power suply? or a socket i put my computer in?i dont think it will be in monitor though

My problem is just the other way around - the computer doesn't start. But if I hard-restart it after it freezes - it works OK.

yes me, too, i mean after hard reset it freezed, then after hard reset it went back on
i still think its has to do something with power suply=P

could there been a usb memory stick in or some?

Nope I don't use one (never have).

after googling i found this
http://www.techspot.com/vb/all/windows/t-8...efore-boot.html
i told you it s in power suply=P

Yep it is the powersupply breaking.