Upgraded to 2.8.1, now can’t access admin panel

Last night I upgraded my blog from WP 2.8 to 2.8.1. After upgrading, everything seemed fine, and I was even able to post an entry at 10:00 this morning; however after that I stepped out, and when I tried logging in again, I was unable to do so. My logon information seems to be okay, because I end up in the admin panel, but instead of the full panel loading, only the top blue bar loads, but nothing else loads. I’ve tried clearing my cache, but that hasn’t worked, and I’m having the problem in both Firefox and IE. I should also note that I upgraded to 2.8.1 on a different site running the Atahualpa theme (the same theme I’m using on the site I can’t access) and had no such problem. I should also note my website (www.bloggingblue.com) seems to be working just fine; I just can’t get my admin panel to function.

I’ve scoured these forums and seen some possible fixes, such as renaming my plugins folder, but if I try to rename my plugins folder, I get the following error message when I try to login:

Parse error: parse error, unexpected $ in /home/content/m/r/z/mrzippy13/html/wp-admin/menu-header.php on line 138

Can anyone help me? I’d hate to lose 2+ years worth of blogging.