HELP! My computer has a virus!?

Recently i let my mother burrow my computer for a while, but when i received it back it came it came a nasty virus. Every time i open a file it would force me into "open with" even when do select the appropriate file type it will redirect me into downloading something called the "iexplorer". Regardless where and what type of file i open it will always redirect itself into this problem. I tried installing malware but every time its done downloading it would state " Application was not found". HELP! Am i screwed?