|How are you inserting a CDROM disc into your hard disk drive? Impossible. ;>)|
It could be your CDROM drive is dirty (the lens etc), the drive has died (it happens), or windows has hiccupped and lost some of the parameters for the drive. In which case (the latter), if it's an IDE/EIDE/ATAPI drive, you would open Device Manager, and remove the CDROM drive from your system. When you reboot, the hardware wizard will start (providing the electronics on the CDROM drive are functioning), find the drive, and reassign appropriate parameters for the drive.
If your system is dirty, it's a simple matter to open it up, and use compressed air (outside preferably) to blow out the dust from the system/components/power supply. I also use a natural animal hair, 3/4" wide paintbrush to gently "scrub" the board/components. (Synthetic hair paintbrushes can cause static electricity which can harm electronics.)
If you deem the above too risky for you and take it somewhere for "cleaning", it's ~unlikely~ you would loose files/data, as long as it's a reputable place you take it to.
It's a good day when you learn something