If it worked before, I'd recommend restoring your pc to a date/time when it worked. If that still doesn't fix it, then try these troubleshooting steps (go to the next step if RenegadeX still doesn't work):
1: Redownload, then reinstall Renegade X
2: Check video drivers and do a clean installation
3: Update Directx
4: Check for hardware problems (CPU, RAM, HDD errors)
5: If EVERYTHING ELSE FAILS, and IF you can, reinstall Windows.
Any other suggestions guys?