Do you have a manul for your machine?
you can download it from here http://www.singerco.com/uploads/download/467_7466_efs.pdf
I can't see anything relating to error message 88 in the manual.
So I would suggest you start by trouble shooting the bobbin case, go to page 76 in manual and folloing images, take out bobbin case, clean and replace it. Turn machine off first and once its back in turn it on and see if the 88 code has reset.
Then redo bobbin winding, and threading up. Start with the manual instructions on this page 18 and 20 and work through it step by step. Make sure bobbin is in the right way so thread is feeding off in the right direction. Also just a thought, you haven't got a stray bobbin in there that isn't a Singer one??
I hope that this helps you to eliminate your machine problem, obviously if this doesn't solve it you may need to take it for a service and see if the 88 display relates to something within the machine circuitry.