engine locked up

[yamaharacer911]

i got my bike out of the garage i was messing with the airscrew i think it is. then i gave it gas and just putted slow around my front yard in first gear then i was like alright its seems to have alot of bottem end so i took off and it was real slow when the powerband was suppost to kick in so i gave eit more gas to see if it would go and it went brrrrrrrbrrrrrbrrrrr so i tried to keep it from stailing out with the gas and it just locked up the back wheel. so it wouldnt let my kickstart it so i put it in nuetral and pushed it home.my dad took it apart because i didnt want to mess with it he told me the piston moves up and down i figured he meant up and down on the crank but he meant it moves in the head so its not seized. i took a look at it the oil its light grey and the crank wont move any ideas thanks for all the help

the bike is a 2002 yz125

[CamYZ125]

So, the crank won't spin at all? And you're sure it's in neutral?

[yamaharacer911]

the crank wont spin at all i can roll the bike in neutral yes

[jim slim]

If the oils light grey you either have a coolant leak in motor or you got water in the oil.