why won't client connect to server?

My workplace has three pc's set up for paid internet use with cybercafe pro 3.7 software. All were working fine for a few years, then suddenly one stopped connecting. Have checked connections at back and all are fine. Even swapped cables with working machines to make sure wasn't a cable problem. Read somewhere that right clicking and deleting black screen might solve it, but just deleted screen altogether and it never came back again. The pc in question starts up and loads most of the screen with the software info, but red button at top says trying to connect to server and the timer on the screen is frozen.