I have an 8' fluorescent fixture in my garage and when it wouldn't come on the other day I assumed the bulbs needed replaced so I put two new bulbs in and still no light. I have checked the power going into the ballast but don't have a clue as to how to test the ballast to see if it has gone bad. Any suggestions will be appreciated. :confused:

How cold is the garage? Some fixtures are not rated for low temperatures. It is well below zero here and none in my garage will come on, but they all work again when it warms up.

If you have 120 volts to ballast input, and you have good bulbs, and there is still a problem, it is either a bad Ballast or bad sockets, Or the new bulbs are bad.
I think the ground is important for flourescents to get a push against the high voltage.

All ballasts and lamps have minimum temperature operating ratings. This is usually listed on the ballast labels. Not so on lamps, but will be listed on the lamp data sheet provided by the manufacturer.

Zero is much lower than the typical 50 deg F rating of most ballasts and lamps.

The ground is needed as lamps must be within a certain distance of a grounded surface, since the lamp and ballast utilizes the capacitance between the lamp wall and the grounded metal surface for starting purposes.

Each ballast as it's own specs and test secondary voltages, published by the manufacturer.

If new lamps don't help, and all the connections and lampholders seem to be in good shape, all we do is replace the ballast.