Have you used the folding tongue recently? It's not uncommon for the flex line to get pinched which can cause some strange problems.
If not then start by checking your brake fluid. Is it full? If so then you probably have an issue with the master cylinder. It could be a bad shock or a bad diaphragm. If you're low on fluid you'll need to find out where the fluid went. Most times if you you're losing fluid it going past the seal in the caliper or one of the flex lines is leaking.
If you have the MC trailer I believe they were still using Reliable in 08. If so repairs are going to be tough without converting to the UFP set up as parts are getting scarce for Reliable products.