In this case I would just start with an electrician. I think if it was my house I would do a service upgrade or at least replace the panel.
If this is a rental the fix may be to run a new circuit into the computer room with a grounded wiring method. Strange things happen when there is no ground present and your system goes looking for one through the phone or cable line.
The next thing is to look at the Dmarks for the other services to be sure they are grounded to your electrical system grounding electrode. You do not want to see separate grounding electrode systems. Again any ground shift will show up in your computer where the different systems come together.
