My computer was infected with 38 viruses at my online bank

today l logged in at my online banker. After logging in l got a message to increase my security. Before doing so l called the bank. They said, yes, the software site is legitimate. So, l downloaded it. After l was done my computer self destructed. l have 38 viruses and cant even open anything from my task bar. l have looked to un-install, but there is no program as such to uninstall. They have a site instructing me to buy MS Removal Tool. Please somebody help me. My computer is a laptop and only 2 months old.