If I have 2 computers that are running, and I constantly switch back and forth using a KVM switch to switch monitors (and mouse), is that a problem?
Can I blow a video card or short circuit anything?
No, that should not be a problem. After all that is exactly the purpose of a KVM switch.
The KVM switch (that is operating properly) should properly load all PC connections so that nothing bad happens.
Note: I've used KVMs powered externally with a wall wart and powered from the connected PCs (the power from the keyboard and mouse ports). The PC-powered KVM switches have one less cord, but the externally powered ones seem to operate more consistently. YMMV