None IT person needs some advice!

This is a really basic query I’m sure but any help would be appreciated. I am unable to get to my desktop when I turn my computer on because my mother-in-law inserted a disc, it began to load (an AOL connection disc), then changed her mind, took the disc out and inserted an NTL disc, but while the AOL screen was still updating. Now when the computer is turned on it says ‘please wait updating’ and nothing else will happen.

Can anyone spend a quick couple of minutes advising me how I can rectify this?! Thank you 🙂