HELP - My Sewing Machine is NOT SEWING - the Thread keeps Bunching up on the Fabric/ What could it be?

I haven't used my Sewing Machine in about 4 years - so I oiled the parts and it seemed to be working fine - but when I try to sew -it gets BUNCHED up - as far as I know everything is inplace and the thread and bobbin are in correctly - but its been so long - I could be doing something wrong -I guess But I am making my daughter's Easter dress and I'm running out of time - What could be causing this and what can I do to fix the problem - should I just take it to a Sewing Machine Repair Shop ? Its a Pro-Sew brand Sewing Machine only 6 years old and I dont have my manual - can I find one online maybe ? Any suggestions ? HELP