Problems without ground, Amplifier & Exploding surge protector?
Have you checked the voltage at the outlet?
Your guitar amp may be 120 volts AC only, while most computers use switch mode power supplies that can function with anywhere fron 100 volts AC to 240 volts AC at the input.
If the outlet supplies significantly more then 125 volts AC the switch mode supplies in the computer gear may work fine but any device rated for 125 volts AC (or a bit less) will, at best, blow the AC line fuse.