when i press f8 in win 7 i have the option of 'run safe mode with command prompt' but it does not work on choosing it.
I'm not very good with these commands, so I had to try it. When I start with F8 this way, Windows loads files, and then I get this black window, sort of DOS type, and it says cmd.exe. No normal desktop is visible, the surrounding of the windows is black, only with Safe Mode typed in the four corners.
I can, however reach the cmd.exe via Windows' normal Safe Mode, by typing cmd.exe in the Search for files and folders, found through the Start button.
one thing more i can not run my operating system in normal mode and not have win os disc.
Many factory made computers come with a separate disk partition that contains Windows; it has substituted the physical / separate DVD. It depends on the make of your computer. There may, probably or possibly, be everything for fixing the system. These tools provided, if they exist, may be more customer friendly.
Don't know if this helps. But perhaps you could try to start with plain Safe Mode? Or do you have the option "Repair Windows" with F8?
David's #1 is quite good too. Might be the easiest? When using a Restoration Point, do check what Programs will be affected - you'll need to re-install them.