I would HIGHLY recommend MSE (Microsoft Security Essentials) for your A/V, and the free version of MWB (MalewareBytes) [the paid version adds real time protection]
I would also recommend using multiple accounts, with passwords, on your machine per regular user. Do not enable the Guest Account for non-regular users but rather create an single account for them and password it.
Something else I would recommend would be some type of browser protection.
Adblock Plus or µBlock for basic protection. If you are feeling powerful and up to learning something new, HTTP Switchboard is a catch all in my opinion; be warned, it has a learning curve, but it isn't THAT bad.