Slow browser, slow internet, random audio ads: virus?

Glad you got it sorted. Have a look at this tutorial, a system image can be handy to have when something like this happens:

Backup Complete Computer - Create an Image Backup

Also, browse some of the tutorials here, you'll find many excellent articles and tips:

Tutorials - Windows 7 Forums

MSE releases 2 -3 updates daily, so keep that updated. Malwarebytes is an on-demand scanner, so run that regularly & also keep it updated (New defs are released daily)

This what I use and it has worked well.
1. MSE
2. MAM Pro
3. Windows 7 built in Firewall
Filehippo Update Checker
4. Cclean/Tool Box to check things that might of slipped in. Programs, Startups, Restore points, ect.
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NO Torrents
NO P2P
NO Tuneup what ever programs of any kind.
ALL programs on my computers are legal in every way shape and form. Some paid for and some free.

Tienjt said:

Oh, and I believe Win7 came pre-installed on my laptop (there's a COA sticker with the product key on the bottom of the laptop), so I don't have an installation CD or whatever. Any options?

You might also check with the person who first "owned the computer" ... since you have no actual knowledge of what OS it came with.