Stupid steam. Redownloaded it too (and it still didn't work!). Never had an issue with Steam until today and they're taking their time on a fix...
Downloading a Beta Client and will patch up I guess. Steam's Key they give me on the second should work regardless.
I WILL DESTROY YOU STEAM!
Steam seems to be having connection issues ( it seems form other posts ) try this. turn off steam, then go to my computer, find the steam folder, should be steamapps then go to the STO, and use the STO.exe. make sure steam is turned off.