Yup, it needs a working battery to start in normal cases. You can try turning it on, and doing a quick off/on flick on the PSU. That should give it video without the battery. If you want a battery, Fry's in Sunnyvale sells them for $6.

IMO, you should try and see if it works without that cap, but don't toss it. There is a chance that it might not be needed at all.

and in regards to the overclock switch, it doesn't matter; the switch settings are most likely for different CPU speed settings.