I have cashed out my 401k to invest in a home. The deal did not go through and lost $3,100.00 on the attempted purchase.

The holding company of the 401k withheld 20% of the money to send to IRS. I have been living on the proceeds of the 401k for 6 months. I did have a job before the cash out, made about $9200.

The amount of the cash out was $36,000.00 with 20% withheld, it was $29,880.00.

My questions are these.
Do I owe for Medicare and Social Security on the $36,000.00? If so how do I calculate based on this information?

You owe NO Medicare and Social Security; those taxes were paid when you made the contributions to the 401K.

You do owe a 10% early withdrawal penalty in addition to normal taxes.