Have you scanned for malware lately?
is the Windows HAL (Hardware Abstraction Layer)
Caused this to crash:
Ntkrnlpa.exe is part of the Windows Kernel as are Ntoskrnl.exe and ntkrnlmp.exe. These files install as part of your Windows NT/2000/XP/2003 operating system and are needed at boot time. You'll find them your Windows\System32 folder. Trying to disable or remove these files could have undesirable effects. You'll find more information at http://support.microsoft.com/kb/887675
. You'll find information about a vulnerability in the Windows Kernel involving these files at http://support.microsoft.com/kb/931784
[out of date info somewhat since 7/8 aren't listed but....]
If the kernal gets corrupted, you can try a system repair, info is in tutorials, if it fails you have to wipe and drop a fresh 7.
But I'd be checking for malware before going there plus it could be RAM causing issues, and without checking that first, no amount of OS repair/reinstall will stop the problem.