Huge Logic Express Problem

I have been using Logic Express for about half a year with moderate success on my 1.6ghz Power Mac G5. Several weeks ago I began to have a recurring problems with my computer. Logic was not performing and other apps were crashing so I updated to Tiger. I did not clear out my HD, I upgraded. At first it seemed that most of my problems with all apps were fixed and everything seemed snappy, but then I began to have a major problem in Logic.

When I would open the program after one or two seconds the screen would come down that says " you must power off your computer or press the restart button" in every language. I took my problems to these forums and one person said that it was a common problem with Tiger that could be fixed by upgrading logic to 7.1. So I bought the upgrade disc and installed it. It fixed nothing. The problem happens at least once a day and beyond that, the program crashes up to once every 10 minutes.

As a sidenote, I take very good care of my computer, running proper maintenance on it every couple of days. The HD is damn near empty and it has a gig of matched RAM. Before I upgraded to tiger I got rid of every kind of mod/haxie or system performance utility that wasn't made by Apple and I still keep the system running as close to factory as possible.

Now an even larger problem is happening in logic. I use an M-Audio MobilePreUSB as an audio interface between mics, the computer and studio monitors. Today Logic started having a problem where it stops playing and says that the MIDI and the Audio cannot be clocked to match each other or somesuch thing. When this happens no audio can be heard from any source on my computer through the speakers. Even resetting the Audio Driver in logic and in system interface and Audio MIDI setup does nothing, so I have to reboot my computer.

With all of these problems, my computer (my first mac mind you) which I intended to last for years has become nigh useless. I'm going to University this fall but before than I need to record a large amount of Audio for a CD, so I need to solve this problem soon, and I need the computer to not crap out on me if I need to use it to write an exam.

Any posts are welcomed.