Of course it's trivial to say that, but it can't hurt to check your scanner cable connection. See if all the connectors are properly connected. Also you might disconnect your printer for now to erase any possible conflict in advance. See if your scanner is properly connected to the power line. If you want, you can also check if the parallel port is securely fastened to your computer tower. On some PCs these tend to get loose or the metal holding the port in one of the PCI slots is sometimes overly weak. You might find that attaching it in one of the port-shaped holes (probably you have to break out the covering metal first) is a better alternative. But for now just checking the cables will do fine.