Yeah, you should download an anti-virus program if you don't have one already. You should also download Malwarebytes
and a spyware detector like AdAware
Once you run all of these programs and clean your system, test again, if you're still having trouble loading your start menu then you can start diagnosing WIndows services to see if they're the problem.
Go to Start > Search "msconfig" > Enter
Now choose a selective startup and disable half of the services. If you computer boots normally, then you know that one of the services you disabled was the problem. If not, enable the services you disabled and disable those you did not. If you boot properly now, you know the bad service is in the secondary list. Once you find the bad service you can search for a solution via the web or just disable the service permanently.