>>1872194Pawls are not engaging. First determine if you have freewheel or cassette.
In my experience, cold weather (single digits F or below, maybe?) will cause a freewheel to freeze up, but I have never experienced this with a cassette.
If it's not the cold weather doing it, then it is a matter of the internals (of the freewheel if you have a freewheel, or of the freehub if you have a cassette) being dirty, dry, etc.
If flushing it as other anons suggested doesn't work, you have a few options: Disassemble, clean, grease, reassemble (which I have never done myself, and is probably a fairly advanced procedure if you have no mechanical experience), or replace.
If you have a freewheel, that's quite cheap to replace.
If you have a cassette, then you'll have to replace the wheel's hub (and since rebuilding a wheel is expensive unless you do it yourself, this realistically means replacing your entire rear wheel, albeit you'll still be able to use your old cassette, tube, and tire).
Whether you opt to disassemble, clean, and rebuild or replace depends on mechanical experience, and how expensive of parts you have. If it's a freewheel, I would just replace it if flushing doesn't work; if it's a cassette, I would try disassembling the freehub before replacing the entire wheel, but if you have no mechanical experience you may not want to. Again, try flushing first.
