The symptoms you mention are common with read/write issues. I've seen these symptoms many times over the years. The electronics within the drive may have been damaged during the shock of the case falling over on the desk.
All of the following can slow a PC to a crawl while trying to read and write.
1) Diskette read/write issues
2) HDD read/write issues
3) CD/DVD read/write issues
4) USB stick read/write issues
It's very irritating (for me that is) to place a CD/DVD (that has no visual damage) in a drive and loose all PC functionality, until the effort of reading the disk finally times out a minute later. Anytime a PC faces read/write issues, the PC will continue trying to read/write until it completes the task or times out...