Pi 3 boots up, but OS is unusable

[Rive]

If you freeze/lock or otherwise crash, then reboot with alt+sysrq+b

Rainbow colored means power issue at minimum, but you still may have a defective pi3. You should be able to run stress, and the Arm should throttle if it hits 80C.

Go get yourself a proper power supply, and try it again.

[Sflamb]

Thank you for the detailed troubleshooting advice.

Going to take me some time to order a new PSU, but I'll post back when I get to do a test run with that.

[Rive]

Thank you for the detailed troubleshooting advice.

Going to take me some time to order a new PSU, but I'll post back when I get to do a test run with that.

Get a good heatsink while you are at it (gonna need one)