Trouble getting into gear...

I have a 1998 Z28 with M6 transmission. The car has been fine till now, but all of a sudden, I can't get the transmission into any of the gears. If I play around with the shifter for long enough, it will eventually go into gear but then I get a nasty whining/grinding sound coming from the transmission.
Anyone ever have this problem? Any input is much appreciated. BTW, with the engine off, the shifter slides through the gears easily.





