I encountered this problem about a week ago, and prior to that shifting into any gear was easy. and now it is very hard to put into any gear whatsoever. Could it be that the Sencros (spelling) are off. I had already went under the car to check to see if anything was caught in the shift linkage, but nothing was in the way.

 

Does it do it all the time or only when the engine is running?

 

Do you have alot of "dead" travel in your clutch pedal.

Do you have a cable tranny? Maby the cable needs to be adjusted.

If you have a hydro tranny, You may have to bleed the line.

 

Clutch is not disengaging properly. Bad hydraulics or old nasty fluid, misadjusted or bad cable. Possible bad pressure plate. If it was just one gear, could be the trans, all of them is the clutch. All answers assume the car was not in an accident in the last week, of course.