Don't worry, Replay Media Catcher has a 30-day unconditional money-back guarantee. But you should always try software before buying, because many companies do not offer anything like that.

What version of RMC and what OS do you have?

If you press Ctrl+Alt+Del, do you see the "MediaCatcher.exe" process and/or the "Replay Media Catcher" application in the Task Manager?

Did it crash for you before? Have you tried to reboot your computer (or just kill the MediaCatcher.exe process) and re-launch it?

Related thread:
Replay Media Catcher SEEMS to vanish when recording!