Problem 1 sounds like a CPU/motherboard/Memory problem. If you have "extra" memory in it, usually it's found on the bottom in a tiny little door lid with a screw. Remove the extra memory. Remove any peripherals, take the battery out and just use the AC power. Take out the cdrom/floppy if it's in there. Remover any pcmcia cards. See what happens.
Problem 2, yes you can remove the drive from the enclosure in MOST situations. Usually it's simply just a standard drive with clamshell and interface.
Problem 3, I would take the drive out and hook it onto an IDE chain like a standard drive. sounds like the boot record is corrupted.
How do you do that?