1. Try the same browser as at work with the same settings in Tools>Options>Advanced (if it is IE).
2. Maybe the site did an IP ban to ban you. That's easy to check. Find a laptop that works at your work and try that at home. If it doesn't work there it's related to your connection or IP-address. Then contact the webmaster of the site.
I work on an HP G7000 laptop at home which runs Windows Vista. For exploring I use IE 8. My problem is that when I login on certain websites' memberpages which I use regularly, it keeps on bringing me back to the login page with an error message that the user/password is incorrect or with no error message, EVEN though I have made very sure that I enter the correct username and password. When accessing these websites on my work PC with the same information there is no problem and I can enter as member? What should I change on my laptop's setting so that I can enter these pages?