Here's a cheat sheet of how to fix crashing ArcMap. An ArcMap "crash" is when ArcMap abruptly closes, or closes with a popup referencing an application error.
Stop going down the list when things are working again. Good luck!
If you get crashes on one mxd or dataset the mxd or data may be corrupted. Copy your layers, start a new blank MXD, paste to the new data frame. If it's a complex MXD that would take a lot of time to rebuild from scratch, try to repair the mxd with MXD Doctor. Back up your data and try to rebuild a dataset that is making things crash.
Is there an system resources issue? (full C drive, %TEMP% pointing to a non-existent folder, etc)
Can another user log into your machine and successfully do the workflow without a crash? If so, Reset your ArcGIS application profile (first, try a rename of Normal.mxt, then whole ESRI profile, then the registry)
Make sure your display adapter drivers are up to date. This is a likely fix if ArcMap fails on startup when ArcCatalog starts up just fine. (One time I actually had to downgrade a very new display driver to get things working, but usually the most current is best.)