A1200 crashes

[AmigaMance]

Download the MCP package from Aminet and install just the mcpramlibpatch in your startup-sequence.
 You can also try to install blizkick with its romfixes module, (you could try SystemPatch too) although i don't think that this will help with OS3.9 .
 Try a newer/different version of the 68060.library.
 If all these doesn't help, open your Amiga and clean it up.

[AmigaMance]

 Oh.. I forgot to mention what could be the most probable cause of the random crashes as you describe them: Some A1200 motherboards have "timing problems" with 68040 and 68060 equipped boards.
 If you search this forum with the right keywords, you will find which motherboards are affected by this problem and how to correct it.