Your net earnings (this year) have to be a minimum of $4640 to receive 4 work credits for the year. Following the link I posted above and read the section on work credits.

Here's the link directly to SS as well on credits: http://www.ssa.gov/dibplan/dqualify2.htm

So, a year you claimed $400--you received zero work credits towards SS.

5 years after might not actually be accurate since I'm unsure of your work pattern come to think of it. But if someone works steadily for 10 years and than stops, they remain eligible for SSDI for 5 years. (If I've done a poor job explaining this, Janke will hopefully correct me.)

Have you determined what your benefit would be if you took regular retirement next year at 62? (It would be good to know for a worst case scenario.)