Help USB jumps on and off


The USB connection of my friend's SGS2 seems to jump on and off constantly when connected to certain computers, where it used to work, but not all.

Both computers are running on Windows Vista, and uses Norton Antivirus.

Her Android version is something like 2.3.6, and she seem to be planning to update it when she can - Do you think that might help?

She have tried two different cables, both had the same problem.
I have seen people suggesting to clean the phone-part of the cable, in similar situations - Could that solve this problem?