changed the cat on my 98 honda accord but know my car will not start

I doubt it's that, maybe the engine doesn't have enough back pressure. This would happen if the pipes were not sealed correctly. We changed the catalytic converter on my Dodge Ram pickup and it doesn't like to start up either. We think it's the fact that the converter isn't sealed properly and we're going to put some rescue tape around the top and bottom pipes from the headers. Hope this helps.

Maybe try resetting the computer?

Sounds more like a disconnected wire or blown fuse, at the very least sounds more electrical in nature and probably just coincidental to the cat change, can't say that 100 percent tho based on your statement and no description of what the car does or sounds like when trying to start it.