internet trouble

[Immi666]

i have two users on my computer. myself and my flatmate. on my user the internet stopped connecting, but on his it was fine. so i set up a new user for me and deleted the old one. new one worked fine this morning but when i came in this evening it was playing up again. i've set up another new user and its working ok for now, but anyone know what the trouble is so i can avoid a repeat performance?

[vehelpfulguy]

It would help to know the operating system Windows XP ?) and how you connect to the internet (dial up, broadband etc)