I installed something bad please help?

Hi, so I was trying to open an avi file and i had to run through some installer but as soon as I gave it permission to make changes to the hard drive some really bad stuff happened really fast. Some text in russian came up on the screen and everything was moving and it all was happening really fast so i just unplugged my computer. How ****** am I? Am I being hacked? What can I do in this situation? Thanks in advance.