If you try and run it with the pitch control out of its usable range it won't start up properly, or it could be that you've broken the power switch. Its pretty common on an SK1 that it gets mysteriously locked up and the power light stays on when the power switch is off. Usually turning it on and off a few times will fix it but not if the power switch is buggered.
Alternatively, turn it off and try discharging all the caps by shorting their pins together, especially that big one over by where the batteries wire in.