[Coda]

Unfortunately, contrary to common wisdom, defrag doesn't do anything but waste time. Defrag is a performance optimization tool, not a system maintenance tool, and the optimization is very nearly irrelevant considering you'll lose more time to the defrag operation than you'll gain in runtime performance over the lifespan of your computer.

Uninstalling programs is a sound idea, but freezes and system-level crashes are usually driver-level. Honestly the best thing you can do right now is to back up your data and reinstall Windows from scratch, then reinstall the programs you actually care about. (NOTE: Don't back up programs! Reinstall them from the original media or download them fresh! Restoring programs from backup is dangerous (what if they're infected?) and unstable (programs expect their installers to be run the right way).) If this doesn't fix your crashes, it's really not fixable.

Sadly, your experience is "well, that's just Windows for you" in my book. I've never known Windows NOT to do that.