This is the easy way (as in least amount of understanding required). Though it does take a fair bit of time. It won't keep the professionals out but should be adequate to keep the script kiddies at bay.
1) Save any important documents to an external drive
2) Give them a good scanning with a clean (up to date) computer to clear out any malware (virus, adware, spyware, root kits, etc...)
3) Disconnect computer from Internet4) Format & reinstall Windows
5) Install a 3rd party firewall from a disk (Zonealarm, Comodo, or whatever). The Windows built-in blows
6) Install Anti-Virus & Anti-Spyware scanners (be sure to include Windows Defender along with whatever happen to be your preferences)
7) Reconnect Internet

Update everything (Windows, Office & Scanners)
9) Fix router settings (if you have one)
10) Reinstall Software and Data
Hopefully I didn't forget any steps
