[re "mode switch" malfunction]
>I turn it on and it comes on, then shuts off. And then when I turn it off,
>it
stays on for a short while before actually shutting off and I couldn't
even get it to stay on long enough to get a picture.

Any ideas and how would I get to the bottom part of that button? Anyone
been that deep into the camera?<

Yes, this is a well-known problem. The switch is called the "mode switch".
The best fix is to replace it, but you are probably looking at $90, plus $20
or so down the road for a new battery compartment. It would be cheaper to
buy a non-functioning 990 on eBay as a parts camera, if you could first
verify that you are not getting one with a defective mode switch.

The recommended procedure is to clean the switch lightly with residue free
contact cleaner. Don't experiment with different solvents - the one to get
is DeoxIT D5 from http://www.caig.com/.

Start by applying a small amount of the cleaner around the shutter release
button - use a toothpick and don't use more than a couple of drops. More
than that and you may affect the operation of the shutter release membrane
switches. Work the mode switch back and forth until the contact improves.
if the problem is slight corrosion, which yours may be, this could restore
the camera to normal operation for quite some time.

If this does not do the job, then you can indeed "go deep" - here's the
procedure for the 950, predecessor to the 990:
http://www.nightskyevents.com/Nikon950repair.html

The switch itself is a piece of work - multiple layers of folded ribbon
cable, two membrane switches, and a rotary wiper switch, all in less than 1
square cm. Very difficult to take apart and get working again - I've tried.
If all else fails, and you don't mind having your camera look like something
out of Mad Max it would certainly be possible to rig something with an
external multi position switch, or a small inline DIP switch soldered to the
ribbon cable.

Best of luck - I have probably taken more pictures with my 990 than all my
other cameras, film and digital, combined.

Mike Russell - www.curvemeister.com