Over a year? You need to contact who ever is doing it as they found something, or think they did, they do not like and are deciding on what to do with you. That is what happens most of the time when it takes that long.
Is your spouse not a US Citizen or you ever had mental treatment? Those are 2 things that come up, besides the money issues.
There's a hiring freeze going on.
Depends on the agency and location. Unless http://www.usajobs.opm.gov/ is fluff, there's quite a few govt jobs available. At the agency I work at, I was told there was a hiring freeze at least in my region, but I noticed an open office position over in another region/state *shrug*.