Alright, first of all I have no clue about your video capture problems. Never used one so can't help you with that.
Now, my impression is you are having issues with possibly a bad CD ROM not a bad hard drive, but we can test and be sure.
Download the appropriate hard drive testing software for your make of hard drive from this link: http://www.computerhope.com/cgi-bin/yabb/YaBB.cgi?num=1122425778
This will test your hard drive for bad sectors. Usually, if you have less then 5 sectors just let the diagnostic "isolate" them and continue using the hard drive, testing it again every month or so. If it reveals more then 5 bad sectors it is time to consider buying a new hard drive. If your hard drive keeps developing new bad sectors this can cause you all sorts of issues and should be replaced.
As far as whether or not you should return it to the shop, consider this. If your computer is off warranty and they are charging by the hour then maybe you should follow some suggestions people give you here first. If they are being nice and checking your computer out for free and you trust them, then why not?