pc won't boot after registry cleaning

I ran a registry cleaning and when I turned my Dell (windows 7) on here is what happens:

the black screen with one cursor line in the upper left hand appears, as is normal. However, it takes at least half an hour to move to the next screen.

The next screen shows the progress bar, but it moves extremely slow. This is the same screen which shows the two options from F2 and F12 (setup and boot options).

it takes at least a half hour to advance to the next screen.

The next screen is the "Windows is starting" screen with the Windows logo. I let it run for over twelve hours like this... it eventually just was a black screen and the hard drive eventually went into hibernation mode and wouldn't do anything else.

Please help!

not being able to get Windows started is going to be a severe hurdle but let's see what can be done.

does hitting F8 to get into Safe Mode make a difference?

can you get into the BIOS settings (hit F2) and see if any setting stands out as needing tweaking? (boot order, clock, drive detection etc)

during all this waiting, is the hard drive light continually flashing?

any chance you can remove the drive and connect it to another PC to test the hard drive.

what about booting from a USB or DVD with some other OS on it? say some Linux distro, or Hirem Boot CD and load up MiniXP.

You can actually repair a lot of windows problems with a Windows install CD. In this instance you'd boot into the Windows Install CD, select Repair My Computer (assuming one of the automatic repairs doesnt fix the issue,) select command prompt and you can run a few commands that might help you boot,

C:

bootrec.exe /fixmbr

bootrec.exe /fixboot

bootrec.exe /rebuildbcd

sfc /scannow /offbootdir=C: /offwindir=C:\Windows