Could be a memory issue, a driver issue, a hard disk issue or even a power issue.
You could try updating your WEI to see if this shows where the drop in performance you are experiencing is coming from. Attachment 189501
This may or may not narrow it down.
Other things you can try include typing "SFC /scannow" in command prompt (in the start menu type cmd, right click and choose "run as administrator" Attachment 189503
Although this will take a while and may need to be done more than once.
You could also run "memtest86+" available here.
which will require burning to disk or bootable flash drive.
Or create a new thread in the BSOD section and follow the instructions carefully.