Windows 7 on?
You almost certainly do not have a virus but you have certainly messed up something.
Try booting from the Recovery Drive and see if there is anything there that could help
Okay. Here is what happened. I tried to install Windows 7 on my Mac with Boot Camp. When it restarted, and went to setup, it couldn't find the install.
I read somewhere that when someone was installing Win7 on a laptop, they had to switch the USB ( I was using a USB drive ) to a 2.0 port. I tried to use http://xoneforum.allen-heath.com/forum_posts.asp?TID=5294&title=macbook-pro-usb-30-issue-fixed to get USB 2.0 on my iMac.
About a few hours later, I couldn't use my USB drive on my Mac and figured it was because of that. I told myself to change it back to 3.0 later.
Today, when I turned on my Mac, both my Apple keyboard and Apple mouse wouldn't connect to the computer. I then tried to use a USB keyboard and USB mouse, but I figured that because of the USB 2.0 and 3.0 stuff, it wouldn't work.
Now, I'm going crazy. My mom thinks I got a virus because of downloading stuff, and it's nowhere near because of that. PLEASE help me I beg of you guys.