I was running Windows XP Pro x64 with SP2. Made a new partition, installed Windows 7 on new partition. On boot, I could pick Windows 7, or older Windows OS (XP Pro x64 SP2, basically Server 2003 SP2).

Thanks, that was the problem. I forgot that about a week ago I had edited my Group Policies and disabled Windows Messenger. I change it from disabled to "not load on startup" and it works fine now.