OK fellow lighting gurus, here's one for ya:
So any ideas why a F96 slimline won't light lamps but the ballast hums when power is applied and lamps flash dimly when power is removed? Scored some slimline fixtures and both of the two I've brought home so far do this...I then tried the set of lamps I was using back in the other slimline and I have (albeit with a broken socket and fussy ballast).  Any ideas why this is? If the lamps had lost vacuum from rough handling they wouldn't flash dimly would they?
BTW the ballasts in question are a 80s full power 1.45a Advance, 90s energy-saver 1.25a Advance, and a Magnetek/Universal WattReducer.  Lamps are 1996 Sylvania F96T12/CW/SS.
And I DID do this in an unheated garage at about 45 degrees...that's cold for 60w energy saver slimline lamps but they SHOULD at least light!!

If there is too cold for the lamp/ballst OCV combination, the result is the lamp won't light at all, the ballast is just not able to ignite it.
That is the main problem on those border temperatures.

You may try to momentarily shorten the ballast, so create an extra inductive kick (when the ballast is running with the lamp connected), it may help to ignite the lamp.

And generally: Check for the usual things with not starting fluorescents, if the amp is dry, clean, the reflector (external electrode) is close by and grounded,...

Yeah maybe it's just too cold...I think I will try this indoors as well where it's like 75F.  And tomorrow I'll bring the other two fixtures home and give them a whirl. 
I did not ground them, however.  I tested using a 2-prong cord actually, but I tried touching the lamps, since that works for fussy ungrounded rapid start ballasts most of the time.  Even tried removing/inserting lamps with power on.  They did not have a grounded reflector nearby as I had the channel covers removed for testing. 
I think I might also try using some junky 34w 4' lamps as test victims to see if the ballasts have output at all.  I see no reason why they wouldn't though.  Maybe one or two of them being bad, but not three at once!

Try using 75 watt lamps in at least 60*.

It may be a bit obviouse but have you checked the line voltage in your garage its worth a check

"Try using 75w lamps in at least 60*" Ha! That wasn't an option since the only pair I have are 60w.  But it was a little warmer today.  I tried them again and guess what? They work! (Including two more of them).  The 80s Advance full power ballast always seemed fussy though in the several months I've had it.  It liked to only light one lamp in the cold.  So I let it do that and ran an errand.  20 or 30 minutes later, came back home and there was the classic wild flicker going on in the garage.  Since the lamps were (kinda) warm I tried a 1.25a Advance Mark III and they lit right up, striating but NO wild flicker.  Ditto for three other Magnetek/Universal Watt-Reducers.  I think that first Advance I've had for awhile is dying then.  Those 80s Advances ARE known to have capacitor issues, which I'm thinking is the case.
I now have a combo of the 60w lamps and the Advance Mark III running indoors in my 75-80* room, and they work great, almost too bright to look at! Totally worth all the trouble I had initially!
I think really cold lamps were to blame honestly. 

When I was still living at my mom's, I had 4 slimline fixtures in the garage, and they have always started for me even when it was cold.  I think the coldest was in the teens, but they sure didn't like being lit with all the wild flickering for a few minutes then it would do the shimmer thing and would never get out of that.  But those were the full mercury GE WattMisers with the red etching.  It is possible that your lamps are just being fussy. I think the ballasts in those were the much older Advance, possibly early 70's.  Now that I think of it, I don't even think the label said "No PCB", but that was 20 years ago.

Yeah I've gotten the Watt Reducers and Mark III to work, and they shimmer a bit but not too badly.  Are those fixtures you're talking about still there?

That is good that you got them to work! 

Unfortunately, those fixtures are no longer there. I ended up taking them down and put them into storage in the loft of the garage, (Mom couldn't stand the cold startup).  I didn't have a place to put them in my first place, and well my sister ended up trashing them.