Yesterday my spy ware software detected and deleted a worm infected files.
Now my Vista - Ultimate will stop booting after the password screen and shows Welcome message and nothing further.

I cannot loose files and data on this machine by reinstalling OS.

Help please?

Try booting into safe mode by rebooting your computer and start toggling the F8 key. If that works then you need to save all your data immediately before doing anything else. Then try to do a system restore.

Save your DATA first. you may not get back in the next time around!