I just got a sewing machine off Ebay. It's a 20 something Kenmore. For some reason, when I try to sew with it, the thread tangles and it won't budge. I have tried adjusting tension on the bobbin and the top thread, and also cleaning out the shuttle. Nothing has helped, and it makes a screeching noise and stops after just one stitch. When I do it slowly, I can't really see much of a problem. Does anyone know what it might be? Or is it time to take it to a repair shop?

:nod Repair shop. You really have no idea when the machine was last serviced or even oiled, a visit to the sewing machine spa will make your machine feel and look like a new woman! :thumb

Or at the very least, you will learn exactly what is wrong with her and if it can be repaired (that is the pessimistic about ebay side of me :eyesroll ). But it is probably just fine.

Karen, who hasn't had her own machine serviced in over 5 years but likes to tell other people what they should do. :innocent

how full is your bobbin? kenmores seem to have a thing for not liking nearly empty bobbins.

My general routine for stuff like that:
take the bobbin box apart
vacuum it out
put bobbin box together
make sure I have the bobbin threaded correctly
try sewing
if it doesnt' work ---> repeat
still doesn't work ---> get it repaired/cleaned/serviced.

but mind you the repair guy charges me 80 bucks to service it and i'm cheap so i try to clean it myself first.

other ideas: do you have the bobbin in correctly?
is the thread threaded correctly (i.e. seated in all the little catches?)

Thank you both. I think that it was the thread tension. I didn't have any idea of where it "should" be, and I think I had it too tight. Not to mention, it does need a good oiling. Would WD40 work?

i don't think I'd try wd40 -- for one it's kinda messy.
they sell sewing machine oil at a place like joanns or hancocks. or a small bottle of similar oil at a local hardware shop might do the trick.