My iPhone 4s connects briefly to my computer, then instantly disconnects. Has happened ever since downloading the ios7 update.

I use a HP Compaq Presario laptop, and have done so for about 7 years. I downloaded the io7 update for my iPhone 4s 3 weeks ago, and now when I try to connect the phone to my laptop via the cable, it connects briefly but disconnects. I have installed the latest updates, both for iTunes and my iPhone 4s; I've tried uninstalling and reinstalling iTunes; I've stopped and resumed the Mobile Device Driver, and I don't know how to resolve the problem. I have recordings of uni lectures that I'd like to put onto iTunes, as well as videos that are too big to email to myself. Can anyone please help me?