Dump your PC in the lake ASAP and buy another one.
Open your wifi connection and tell them you suspect someone near you may have been using your wifi. You didnt know better, and now you want them to show you how to set it up for you. I cant see how anyone would be fucked for anything Internet related unless they break into your home and take your PC for evidence. Unless you used your CC to buy kiddie porn. Whats keeping Joe that Lives next door to Jack, from Jacks Open wireless wifi connection and sayn he is Jack? Remember they have to prove YOU did it. Unless they have your PC to be able to track its you, or if they have YOU on video tape doing what they suspect you did, they have no case.
Come on, murders roam the streets cuz they cant find a body or a murder weapon.
You think they can just say it was you cuz of your IP?...LOL
Dump the PC and get a lawyer... !