Is this a sand along PC or is it in a Network? Stand along means it is not connect to anything. If it is a stand along and u still have Admin rights do the following:
1- change your admin password to at least 16 characters using numbers, small caps, large caps and special characters.
2- change the rest of the accounts to regular users if you don't mind having them or delete the accounts.
3- if it is a network PC disconnect from internet/intranet. Make sure no one can access the PC.
4- update all anti virus and malware, spyware software. Run the anti virus and malware.
5- remove/delete all users.
6- when connecting PC back to network make sure you are using proper security measures.
Usually manufacturers of networking equipment supply instruction to secure your networks especially wireless networks.
