You could also try entering command prompt - run as administrator- type in SFC /SCANNOW. That will look for any corrupted files in the Windows operating system. As far as the BIOS, is there any chance that some of the settings got changed? 
I've had this machine for less than a year, and recently after updating the system has started running extremely slowly. This is very noticeable if there are any video elements playing on any webpage or application. The mouse cursor will drag across the screen, sound will be choppy, video lags, etc.... I even did a fresh install of windows to see if this would resolve the issue, but to no avail.. How would I go about reverting this back to a previous BIOS version? This seems to be the root cause of the problem from what I have read on this page. Thanks.
XPS 8940, running terribly