I'm not on prepaid so I don't have a log on but what error are you getting? Are you able to get to the log on screen (I can get that far)? Have you cleared your cache and cookies? What browser are you using?
If you go to your log in screen and at the bottom there is a link for pre paid customers to use for their log in but when you click it the screen that comes up says we are upgrading our online services etc. and there is no log in. I has been that way for over a week.
Prepaid self service is up and running for me, Brian :) As the others suggested, it might be something on your end.
Edit: just saw your second message. Definitely try deleting your cookies & browser cache as Jorden suggested...