You're saying you cannot even view the parts of eBay that are open to the public?
There are a couple of possibilities:
1. You're on the eBay no-can-see list and that's that;
2. Your cache needs to be flushed;
3. It's a client resolution problem (not very likely from what you describe).
Solutions:
1. Write to eBay moderators swearing eternal fidelity and love;
2. Flush your cache and delete your cookies. If you're using Firefox (and if you're not, why not?), it's Tools >> Clear Recent History >> (Click onto Details to see the list, and make sure CACHE and COOKIES are selected). Then close your browser window, turn off computer, start computer, and see whether the problem is fixed.
3. Click START, then click on RUN, and then type in command. In the Command window, type in ipconfig /flushdns and then hit enter. You may need to restart your computer afterwards.