Computer-Related Plea

I've been having trouble with this web-server as of late.  I had a few heat-related issues that locked up the machine a few times.

Unfortunately, I think it may also have resulted in some filesystem corruption — I just don't know where.  (fdisk claims everything's fine, yet certain files complain that they're missing information that was there previously.)

If anyone knows of a way to force Debian to re-download and install all currently installed packages, I'd greatly appreciate it.  (It's either that or try and tar up all my files and re-install.)