Sounds like either a power supply problem or the harddrive is dying. If you have another p/s unit, try using it instead, especially if you've been using the stock a1200 one. Some harddrives I've used seem to work okay for a while and then start to act up, giving checksum errors or random crashes. Though it's a pain to start from scratch, re-installing your system on a new harddrive also replaces damaged/missing files, libraries, etc. Sometimes, software installers can replace key system files if you don't use 'expert' mode and watch everything.
