Problem engaging first gear?

[Rich2388]

Was wondering if anybody would be able to give me a bit of advice? Drove my car to work this morning which is about a 20min drive and all gears were working fine. Got to work stopped and turned engine off for 10mins, then started the engine again, went to put it in first gear and for some reason it just kept going in to reverse. It was going in to every other gear and pulling away ok but jut wouldnt go in to first. Does anyone know what this could be? If anyone could shed any light on this i would appreciate it. Cheers