I have had that problem before.
The best thing to do is to remove all external devices, except power cord and keyboard and mouse.
Try it again.
If it doesn't work, hopefully you've set up a restore point.
At POST (blue screen with HP Logo) tap F11 repeatedly.
Go to Advanced options.
There should be an option called Restore your computer to an earlier point in time or something familiar pointing to System Restore.
Click the bubble, then next.
Click next again if it says You Must Leave the Recovery Manager
System Restore will take a while to load up don't be impatient!
Restore your computer to an earlier point in time.
On another thought, did you set chkdsk to start up?
Hope this post helps!
