If you still can't log in, try clearing the cookies (temporary internet files if you're on Internet Explorer) and see if that works. Sometimes cookies do weird things to all websites.
Mapleleafgirl72, did you meet the minimum to be paid out, or did the purchase not track? You can submit a cashback claim if it didn't track (it does happen now and again, but not all that often).
For everyone, I suggest using it in a browser you normally don't use (I usually browse the web with Google Chrome and Firefox, but for Quidco only I use Internet Explorer). I have the Quidco-only browser set to clear my history and cookies every time I close it. Quidco can get confused if you've already visited a site and then visit through them, so it is best to keep Quidco in a separate browser.