Thanks all. And yes sorry my sentence was poor. I meant to say the sketch will be powering on or resetting my pc.
It'll be isolated from the PC - I'm using reed relays in parallel with the soft-on and reset switches, and I'll be using an opto-isolator to see if it's already powered on.
I guess with my load being a relay (rather than something that detects signal) the floating nature is less significant, but I'll use 20K pull-down resistors - that way I hope the only possible way for the relays to fire would be from me setting pinmode to output and level to high.
Thanks.