Malwarebytes is good, Webroot is better. If you don't need an antivirus tool then get CC Cleaner. It will go through and delete all the crap that's probably slowing your computer down. I use both of these on my personal and business PC's. Not sure about versions for a Mac if that's what you use, but I'd be amazed if there wasn't.
@Brooke - if you would like I can show you some "best practices" for usage.... and we can introduce you to some of the more 'interesting" tricks of the net and how to have fun
Start>run>type "msconfig" hit enter>startup tab>disable all>apply>restart pc
Internet explorer>tools>Internet option>advanced>reset
Problem solved unless you got a bad virus problem, actually this doesn't actually fix your problem but it should speed up your pc..there's a lot more you can do but that's the most an average user can do
Anyone that uses this fix has to blow me if it works j/j, no dudes