craftgrrl | [EDIT] sewing machine question...

so i just bought a sewing machine a few days ago.
nothing too fancy or expensive, i didn't have a lot of money to spend.
but i'm seriously about to tear my hair out over this thing. it worked perfectly when i was messing around with it, getting to know the different stiches, but as soon as i started a project it started messing up.
every couple of stitches the whole thing gets jammed up, the underside of the stitching looks gross and is a big mess of thread. once the needle goes down, it won't come back up and the thread underneath is getting all caught up on something.
i know it's probably a really common problem or i'm doing a little thing wrong, but the instruction manual doesn't tell me what i'm doing wrong as it's about 2 pages long.
so could someone please help me before i freak out and kick this damn thing down the stairs.

[sorry about text only...i'll have pictures as soon as i can figure out this problem]
thanks in advance.
<3

thanks so much for all the help/responses you guys gave me. i think i've fixed the problem for now but we'll see how it goes. technology and i aren't exactly best friends =)