If you suspect cables (that's possible), try to swap computers and look if problem will follow computer. If computer, which was able transfer 100 kB/s will be able to transfer at the same speed - you may exclude cables and switch. Look for NIC settings, protocols, OS Settings, etc.
If "slow" computer will transfer faster, and "fast" - slower, then problem is either in cable (or in patch cord), or in switch port.
As second step, try to isolate "cable". Try to swap cables at switch. Same asabove, if problem follows the cable - problem is with cable. If not - check for port settings on your switch. Try to connect computers to another ports. If you don't have ports available, try to swap "problematic" computer with another computer and see if problem will follow to another computer.
If you have more questions - send me e-mail.
Good luck.