Acrobat task won't unload and CPU remains 90% busy for nothing

I've upgraded from Acrobat pro 7 to 8, mainly for generating forms with signatures. I'm now monitoring closely my P4 2.8GHz HT CPU under XP PRo SP2 and I noticed lately that every time the CPU activity hangs at 90%there is an ACROBAT task running idle (no Acrobat window opened). Sometimes I can kill the spinning Acrobat task with task manager and CPU level gets back to normal. Sometimes, CTRL-ALT-DEL no longer pops up Task Manager and all attempts to close a session or shut down have no effect. I must RESET in this latter case. I get no error message, no blue screen, just slowed down computer and a CPU that ends up running red hot for nothing! If I had a standard CPU cooler with no CPU monitoring it could fry the CPU on a hot day.
 
I don't recall such problem to occur before I upgraded my motherboard and CPU (HyperThreading).Adobe Acrobat is the ONLY application that is causing such problem. Is it allergic to HT technology ?