Missed it about the CPU fan running 100% all the time.
Make sure your CMOS battery is good because a weak battery can make a system do some weird stuff. If the battery is over 3 years old go ahead and replace it to be sure before doing anything else, if you can pop it out and check it's voltage with a voltmeter. You'd want to see 3.0v's or so with it, anything below 2.9v's is bad and needs replacement.
Although not likely it's possible you may need to reflash the BIOS, something could have gotten corrupted when the issue occured - I really don't see how but it's a possibility.
Related to the above a weak battery CAN cause corruption of the BIOS.