>I tried modifying my project file and when I tried to open it - error message appears - project file is invalid. Is there any way I can retrieve it somehow? I don't have a backup for it, shux!

In addition to Vlad's suggestions... if you do need to re-create the project

Just add the main.prg (or whatever it's called) into a new project then build it, it will add all the files referenced throughout your system

Only problem with this technique is if you are running forms or prg's by using variables or table references
eg.

do form (lcMyform)

they won't be added to the project automatically.

HTH