First, simplify the computer system as much as possible. Determine if the computer is noisy when turned on with no keyboard, mouse or monitor. If it is, listen to the sound, preferably using an SSB or CW receiver. If the noise is a broadband hash, decreasing slowly from band to band, it is probably the power supply. That is what I heard.
Ferrites are the easiest to use.
Do not substitute snap-on beads or other unknown materials unless you are understand how to use ferrites. Unfortunately, it may be necessary to remove one end of cables with large connectors. If it doesn't cure the noise, try an AC-line filter next. That should take care of most cases of power-supply noise. Even those that do have EMI components are not usually as effective as a standalone EMI filter.