If I buy virus protection, will it clean up old stuff?

Welcome to WindowsBBS

To clarify - when your subscription to a particular antivirus expires this does not mean that you are unprotected - on expiry you cease to receive definition updates.

You have a few options ...

Renew your existing subscription - this obviously involves a cost.

The alternative is to use one of the many free antivirus/antispyware programs available - I would recommend Microsoft Security Essentials - free

You should not run 2 antivirus programs on your computer so if you decide to use the free software above your existing software should be disabled or preferably removed.

Generally uninstalling it through Add/Remove Programs is sufficient, but there are cases where a Removal Tool is required to get rid of all the remnants. There is no charge for these tools, but we need to know what your current antivirus software is to point you to a download.

I have moved your thread to the General Security forum which is more appropriate.

The question of your computer running slowly can be addressed when you have sorted out your antivirus.