There can be 1001 reasons. You need to be more specific. Does it freeze all the time, or after a period of operation. When you are using any specific programs. Is there any unusual noise coming from the comp. When was it last cleaned inside. Could it be moist inside? TYpe and model od computer? The more information you provide, the more likely one of the techies will recognise your problem.
Starone, im getting the same problem, Ive tried everything, im looking at a format and re-install to see if that helps. When mine freezes I have to do a hard re-boot. Grrrrr
Many moons ago when I used to use Explorer browser, my computer would freeze a lot; that got on my nerves so much. Since I've stopped using Explorer browser no more freezing.
As wildwood says, there could be 1001 reasons – one I have encountered is intermittent connection of peripherals to the PC (keyboard/mouse/usb devices etc).
In olden days, unplugging a usb device (unannounced) was guaranteed to crash Windows 98. XP and later operating systems seem to cope much better – but I have still seen the occasional crash due to movement of a connection to the PC motherboard.
Therefore I would recommend you take a look at the rear of the PC (with the power off) and make sure all connections are secure (fully pushed home) and not strained.
Thanks for your answers everyone. I couldn't get back to you before because the bl**dy thing kept freezing again. I shall try everything but first of all I will do Hymies suggestion, as being the easiest solution. Will let you know if it works.