How big is the data merge in question and how powerful is your PC?
Try doing half of the amount of records for the data merge and see if it crashes.
If it doesn't try doing the other half of the records and see if it crashes.
Depending on which half is crashing - keep halving the records until you find the culprit record(s).
If both are crashing try doing in multiples of 20 or 50 or 100 depending how large your database.
Let us know how you get on!