Login goes to blank page

I was working on adding some modules to my website the other day, and had just installed the following modules:

browscap-4.7.x-1.x-dev.tar
buddylist-4.7.x-1.x-dev.tar
chat-4.7.x-1.x-dev.tar
statistics_filter-4.7.x-1.x-dev.tar

Once that had been installed, I logged out and re-logged in. Once I clicked the log in button it went immediately to a blank page, URL states index?destination=node%2F01. Another develloper was still logged in, and he disabled the modules that had just been added, but to no avail. I then deleted them directly from the server in the hope that this would fix the problem, but it did not. I contacted our webmaster, who said it was not a problem with their databases, they recommended that I revert to a previous version of our .htaccess file in the main directory, but again, this did nothing. Does anyone else have experience with this problem? It is quite difficult to diagnose since noone who manages the website can log in anymore...

The problem can be recreated by going to http://www.chandleytech.com/user/register. Once there, requesting a username/pw will yield the same results (note: Im not trying to get people to register, this yields the same result as what I get when trying to log in... type whatever you want in the email spot). This leads me to believe that the problem is with the user management system, especially since the rest of the website seems to be unaffected...

-Note: we upgraded to Drupal 5.0 hoping that would solve the problem... it did not.

Any ideas?