Shifting Problems

I just bought myself a yz 125 and am pretty green with bikes. While riding today in the sand pits, I would try downshift from 2nd to 1st in the corners and the bike would go from second into neutral and made me almost wipe out a couple times. Does this sound like gear problems? Clutching? Any help would be appreciated.

I just bought the bike, so I don't know exactly how many hours are on it, but I think the clutch was fairly new. Now I can't even get the bike into first gear, even when it is shut off. I can ride from 2nd through 6th, but no first. I changed tranny oil and I was able to get it into first twice. I was excited so I geared up to go for a ride and it wouldnt go back into first. Nuetral, 2nd-6th is what I got.