Bare, bare, bare minimum, run sp_who2 to see if you have blocked processes. From there, you need to delve into all the skills of troubleshooting and investigation. Without at least the ability to collect data on what's occuring on your system you won't be able to post questions here, let alone fix your machine.

As others have said, spend time with performance monitor and setting up server-side traces through profiler in order to gather data.