Drives not recognizing discs

[jamerican]

All of a sudden, none of my DVD drives (internal, Pioneer and Benq both external) are recognizing any discs - blank, recorded or commercial - inserted into them. PowerDVD says there are no discs in the drives, CloneDVD says no media present. I used the drives earlier this morning to copy some burnt discs and they all worked fine. The only new program that I installed was the latest version of CloneDVD 2. I have since deleted it and reinstalled V 2.8.11 which was the previous version. I have used System Mechanic to check the system and it has found nothing wrong. Yet my Mac G5 reads the very same discs that cannot be read on the Windows machine. Does anyone have any idea what happened?
I am not a Windows person. The only reason I use a PC is to do my dvd backups. Any help would be appreciated.
My PC is a Compaq Presario with an AMD Sempron 3000+ and 512MB ram.

[handyguy]

Why not use Restore? Its part of WIndows XP & can put your computer back when it worked right.

[jamerican]

Why not use Restore? Its part of WIndows XP & can put your computer back when it worked right.

Not being a Windows person I did not know of this feature. I discovered it this morning while trying various options. I restored it to Thursday and now it's working fine. You learn something every day. Thanks for the input.

[cyflyer]

would still be interesting to know what you did wrong, so as to avoid same mistake.