welcome to the windows seven forums miffedmolkusk,
ntoskrnl.exe is the NT (new technology) OS Operating System KRNL (Kernel) which to use different words the "dude in charge" one way of simplifying it is.. it is windows (although that is very simplistic, it might explain why it would use the most power from the CPU. USBPORT.SYS is the main driver
for USB (universal serial bus) connections, which are A.)fast and B.) supply 5volts to connected devices, so it would be another power greedy driver. So I doubt that that is unusual (the increased voltage to those two items)
did you run the windows 7 upgrade wizard to be sure your hardware can handle windows 7?
also as Windows 7 requires more labor intensive graphics for opaque type effects, as well as 3D efx, the GPU (graphics processing unit) likely requires more power so your power supply I suppose could be right at the line, teetering back and forth between working fine and the problems.
a full sudden shutdown can also be caused by an overheated or improperly cooled CPU (lack of thermal paste, bad heat sink contact, inadequate fan cooling the CPU's heat sink, or dust caked over the grooves) It is a safety feature to prevent burning our CPU to ash! Sometimes the fan will really run fast (and loud) prior to this type of shutdown.
And I am assuming you do not overclock your system?
I'd also run a full virus scan, if the system can take it!
Hope this helps,