i have a fixture with (2) 48" T8 32W bulbs that has started acting up. sometimes when i flip the switch on, the light doesn't come on for 30 seconds to a minute. there is another (identical) fixture on this circuit that works fine. i plan to open the troublesome fixture, and check all of the connections, but just can't seem to get around to it. also, since it works fine most of the time, i forget about it.
aside from a loose connection, what else could be causing this?
could the ballast be going?
could it be the wrong ballast in the fixture (i have not looked at that yet either)?
i don't know how old this fixture is, but it's been working fine for about 4 years, only changed bulbs once in that time.

thanks in advance