Do you remember what files you deleted ?
Are you able to choose the windows advanced boot menu ? Turn the computer on & start tapping F8 key .
What computer is that (Dell, HP, Gateway...) and how old is that?
Please try the steps below .
Start the computer and keep tapping the "F8" Key on the key board.You should get a windows called"Windows Advanced Option Menu".
Once you have this window use you "Directions Keys " on the key board to move up to "Safe Mode".Once Highlighted on safe mode hit the "Enter" key.
Check if your computer starts in Safe Mode.
If you are able to get to the desktop.Then go to Start-->All Programs-->Accessories-->System Tools-->System Restore.
Once you click on the System Restore on the windows that loads select"Restore My computer to an Earlier date".
On the calendar select a date that is highlighted prior to when the problem happened and click on Restore.
This should restart you computer and then boot back up.
Check if you are able to login to the computer Normally.