Clutch problem. Not fully releasing, so problems with master/slave cylinder, clutch linkage, clutch itself, or even oil on the disc will cause it not to release fully. Air in the system will cause it not to release. Changing the oil in the trans might make it easier to get into gear, but still does nothing for the not-fully-releasing clutch. Bleed it if possible, check all you can for leaks, bent/loose parts, then either take the clutch out yourself, or find someone who can.