Hp 6715b laptop intermittant 'unresponsive during restart'?

[lectrocrew]

 This is on my HP Compaq 6715b laptop, turion x2, Vista Business, 8Gb ram, 320 Gb HD, Folding @ Home v7.2.9 SMP2.
I've had this issue for several months but haven't really addressed it since it is rarely shut down / restarted. It's only function, pretty much, is running Folding @ Home for our Computer Hope team (67290) 24/7. But I do keep it up to date and sometimes updates require a 'restart'. Sometimes it will restart with no issue. It will always start up after being shut down! But frequently once the restart is initiated it progresses to the point of 'no screen' - then the hard drive activity light eventually ceases to show activity. The only lights illuminated are power supply, power button, and volume mute indicator. For reference those  lights are show in the HP 6715b Maintenance and service guide
Listed on page 16/item #1 (Power Supply) - also page 16/item #1 (power button) - page 16/item #5 (volume mute).
 The machine is unresponsive to an attempt to shut down via power button at this point. The 'control panel' / 'power options' settings is set to 'shut down when power button is depressed'. But at this point the power button has to be depressed for several seconds in order to force shut down of the machine / then upon restart an error message says improper shutdown and gives options of starting in safe mode/safe mode with networking/ normal start-up/ ect.
 I have the original Vista Business installation disc for this PC from HP in both 32 bit and 64 bit and have tried re-installing the x64 OS with the same result. Also now I have installed the x86 OS and have the same issue.
 I have tried several settings in the BIOS startup with the same results - including restoring default settings. I even removed the power battery and CMOS battery before the latest Vista x86 OS install.
 Once I force shutdown via holding down the power button / then restart, everything works fine.
 All software, drivers, windows update ect are up to date, the machine has passed all the HD, memory test I've run,.
 It runs MSE security, Comodo firewall, Malwarebytes and Superantispyware and all full scans show no infections.
 What is causing this intermittant unresponsive state during restart?
 As always, thanks for any help!!! 
Mike