recommend you to take out the coin battery and leave the system dead for 30 minute and insert it back.. and test again..
i currently have problem with my 3 pin fan thingy... whenever i plug in any fan.. the fan blades will go techno shaking
I take from you having a GTX275 that you have Nvida on your sys. do you have installed the performance monitor , Reason I ask is that will tell you temp. of each core of the CPU , I thinking you might have a bad temp sensor in the CPU .