Computer troubles... (URGENT!)

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This past month, my computer has been freezing very frequently, whether it be on shutting down, or by leaving the computer idle for a few minutes while browsing the internet. On top of that, when starting up, I am, probably 4 times out of 5, prompted to press Esc twice for the start up to continue/finish. And if that wasn't enough, my D: and E: (DVD and CD/RW drives) don't seem to be... present. The icons for them have completely dissapeared in 'My Computer', and there is no mention of the DVD or CD/RW drives in the Control Panel (Systems).

I ran a virus check (while also downloading the latest updates), but there seems to be no virus. Does anyone have any ideas as to what these problems are caused by? I also have some pretty big files I need to backup if the solution to these problems is wiping the hard drive, but I can't do that if my optical drives aren't detected!

Can anyone help?!?