another simple (?) problem from newbie

guys, I`ve got problem with clutch.
I always had a problem with geting into "neutral" - to do this, I had to relase a litlle bit clutch
and to accelerate.
but from yesterday I have problems with other gears as well.
not always, but sometimes - when I want to get into 2th, 3th, 4th - I also have to release clutch
and accelerate...
without this - the gears are blocked.
I was said that tightening the "clutch screw" would help...
but, today sth weird happened, after coming back from work,
I had to release the clutch almost completely to make the bike moving.
after riding some minutes, I was not able to move the bike at all.
I accelerate heavily, realesed the clutch but without effect.
the clutch was released completely (and I was able to change the gears)
but the bike was not moving...
I had to unscrew the "clutch screw" (dont know is it good name) to make it good...
what do you think about that?
cheers
Greg