System Repair failed

I have a Dell INSPRION14 laptop OS WINDOWS7.. One day i am Istalling Mac osx Transformation Pack its Working Good and perfectly..after some days I am install another fully Glass theme pack...Theme effect changed by me with select windows explore.exe and .dll etc. Files... It says to complete change plz Restart computer..when i am restarted then computer started but after login only black screen is displayed.. I am using F2 startup Repair, Recovery but all are Failed...i have a No any windows7 DVD..plz help me.. i m From India,Gujrat..Thanks in Advance..

Hi Bhavin,
did you try starting in safe mode? (press "F8" during startup, and select safe mode)
If so, did windows start correctly then?

You say you don't have a windows 7 DVD - do you have a valid license key? If so, you can download the correct image for your version of Windows here.
Also, where did you get theme theme packs from? are you certain they are free form virusses/other malware?

I've seen this before when a custom theme changes or swops the Authui.dll file out.

If you can get into Safe Mode, have a look for Authui.dll in System32/SysWoW64 and check for a Authui.dll back up file as well as the Authui.dll file. If you find one (them) rename so the original (back up) gets used instead of the modified one.

Although if the Authui.dll has been modified and it is the cause of the problem I doubt you will be able to get into Safe Mode.

Your option then would be to go through the back door using a Linux distro on a CD and renaming the files through that.

Elmer BeFuddled you are right problem was occured with .dll file..and Only Two option F2 and F12 are displayed so F8 not working and safe mode not possible...i thik now only one way Format C DRIVE to solve this problem..Thanks for Your usefull Reply..

I would first try to get into the system by using a Linux set up before a reinstall. I use Lucid Puppy as it's very small. Will run off a cd (or usb but I've not tried that method).
See if you can rename the files.