If my father died a few weeks ago and ha a house that has lien attached by the IRS, what happens next?

I am so sorry for your loss.  This is a difficult question to give guidance on with out seeing if there are other assets involved that could possibly help satisfy the lien est., and knowing who else is named on the house.  But the IRS has great power to enforce a lien by seizing property or bringing suit to do so.  So please, get legal help as soon as you can.  Good luck.