Why not formatting your hard drive with the only surviving version of some code and asking "how can I solve it"? What are you asking is pretty much the same.
[EDIT]
First of all, stop working without Revision Control system — these days it makes no sense as such system can be extremely lightweight, reliable and free of charge. Look at this discussion:
Revision control systems, which to choose from?[
^] and also my recent answer with a lot of detail:
Needs some words of wisedom to set up and/or use a server[
^].
—SA