I don't have a CD, no. But I tried to repair the system from the Advanced Boot Menu when I was having the aswrvrt.sys error, and it didn't work.
Maybe it will be different now I've ran a virus scan and reinstalled Avast?
Oh also, I tried to error check the C: drive before any of these problems really started, when the computer was sometimes freezing on startup, but would always boot in the end if I kept trying. I thought it might be an error so I error checked, but then near the end of the check it said something like, 'Insufficient disk space to fix errors' even though I quite a lot of free space on the disk. It kept repeating this message in DOS and I had to power off. That was when the system stopped starting and I got the aswrvrt.sys error. Maybe that was the start. But anyway, should I maybe try to error check again? Why do you think it told me I didn't have enough space? I had 90GB or so at that time.
Sorry to ask so much of you. I really appreciate all this time you're taking to assist me.