G_STRING, also have a look at a program called Spybot which is quite useful at not only removing unwanted nasties but also stopping them once it is installed.
Download | Spybot © ? ? Search & Destroy
My other favourite is call Hitman Pro. It gives you 30 days free before a fee is required.
Downloads - SurfRight This also has a nice utility called Kickstart (works brilliantly with Ransomware) that allows you to make a bootable USB flash drive so you can boot into your operating system and bypass some of the nasties. You can then scan your hard drive and hopefully clean all the rubbish off.
However before you do any of that, go into Programs and Features and remove/uninstall any Toolbar programs, Gambling programs that can be surreptitiously installed and anything else that may be malware. Surprisingly some of these things do actually allow you to uninstall them. If you are unsure what can be removed, make a screenshot of the Programs and Features list and post it here (using a site to hold your photo/image) and we can advise which items can be removed with extreme prejudice.