In such a case, your options are:
1. Do something to thaw the forum out. Come up with a thread idea that will draw so much attention and be so popular that it will draw everybody from all over the internet to this forum.
2. Find a different forum, one that has enough life to be suitable for your taste.
3. Find something else to do - read a book, watch a movie, take a nap, go for a bike ride, go skateboarding, listen to music, learn to play the piano... something, anything. (The preceding options for "Find something else to do" are arranged in order of decreasing popularity with the masses.)
4. Stay on the forum and live with it.
I'm going for option 4 because it takes the least mental and physical effort. Well, the nap would take even less effort, but aside from the nap, option 4 is the easiest.