Help me photoshop isnt working right please help

[Skiwan]

right ive made a pic to illustrate the problem:

ok, at the top of the pic im using the brush tool slowly, and i increased the speed as i went down the image, it should be a curved squiggly line but it isnt.... and for sum reason its draws straight lines..... ive tried reinstalling but that didnt do anything, i need help really bad, i dont know whats wrong with it

 

[lost]

i suggest trying a photoshop forum :S
http://www.eyesondesign.net

those there should know how to fix.