power surge (lightning)... how to troubleshoot?

My computer was recently a victim of lightning. It's a Dell 8400 and it still works but there are problems. The most noticeable issue is that the cpu fan now runs a full speed all the time. The only other problem I've noticed is the USB ports seem to be damaged. Otherwise, the computer boots up and seems to run ok - I haven't done a whole lot with it because the fan is so annoying but I've backed up some data to DVDs.

I've tried swapping out the cpu fan before I realized the usb ports were malfunctioning. The replacement fan had no effect. (What tells the fan how fast to run? Is it something on the motherboard?) So I'm curious how to troubleshoot this further without spending a lot of money on replacement parts.

I guess I should start with memtest? What else can I do? I tried running speedfan but it is only reporting my HD temp... nothing else.

Eh... it's almost 4 years old. Not worth sending to Dell for repair.

Interestingly, I ran SeaTools on it last night (Seagates HD diagnostics). It failed every test. But Speedfan has some of the same tests for the HD and it passes on Speedfan (in "very good" health). I think it wouldn't even boot up if it was as bad as SeaTools says it is.