Had problem with comments. Upgrade created login problem as well

Was using wp 2.2, having restored my old install after a windows re-install, found that comments would never be posted (IE reports an error after attempting to submit, firefox goes to a blank page). Figured I’d try upgrading. So I got 2.7, copied over the old files, and put the db connection info in the new wp-config, and upgraded the database. Now, comments still don’t work and I cannot log in to wordpress (attempting to log in just takes me back to the login page, with both fields blank.. Have cleared cache and cookies, and it doesn’t work in IE or FF. I checked the db entry for wp_users and even put the md5 hash for the password in over itself. Nothing worked. I wasn’t using and plugins that I can recall (other than custom theme if that counts?) and moved everything out of the /content/plugins folder to be sure. Also no error is generated in error.log.