Scanner cannot detect on some computer

I have faced this problem twice. the first time was I am using windows 98 OS on a compaq desktop computer, my acer scanner 310P cannot detect by the computer but once I my friends gateway computer the scanner work perfectly. Now I am using canon FP320 scanner to use on two gateway computer. The PII cannot detect the scanner but the parallel port work properly on a printer but the PIII gateway computer using the same OS (windows 98) can scan using the canon scanner perfectly. So I was wondering what is actually the problem. Was it the hardware or the software problem. Pls reply.. Thank you.