I'm buying a '97 T100 from my in-laws. The truck has been sitting outside for the winter, and had a completly dead battery. So I bought a new one, installed it, and there still isn't anything. The hazards and the headlights work, so I know that there is a connection - but nothing else works: the dash lights, the radio, it won't turn over or even click when I try to start it.

I checked the fuse box in the cab and under the hood but could not find any broken or missing fuses - does anyone have any ideas as to what the problem could be?

Could be a bad ignition switch? Do you have a multimeter? Check fer power at the main fuse (100amp?) under the hood. Does this have any kind of alarm system on it?

Also check the grounds. A loose or broken ground could cause it. Just a guess

Yes, sound like a bad ground or bad positive + contact, check grounds and check Bat. Cables + and - can have (sulfates) inside the cables, looks like a white powder, if you find to much it's better to change cables.
Check for rust bolts, where hold the Negative - cable to the chassis, transmission or body. clean surfaces or change bolts.

Could also be a dead starter. It's not to hard to pull and have tested. I had the one on my '95 T100 rebuilt for about $80 and it only took about 4 hours to have done. It's not to hard to remove, but it is easier to jack up the front end so you have more elbow room. It's on the passenger side of the engine and you'll need an extension and a universal adapter. Pretty easy to remove and replace.