Disable any overclock you may be using.
Backup your sdcard
Insert card, boot into recovery and format the sdcard
Download a fresh copy of the rom you want to use.
Put the rom.zip on your sdcard and run an md5 check, as it is sitting on the sdcard.
Properly wipe the phone.
Install the zip
Download your programs fresh from the market and do not restore any data, except contacts. This is especially important on system settings. Leave it at stock speed until you determine it is stable.
Bad/improper formatting of the sdcard has been known to cause your problems, Always format with the device it will be used in. Computers are more forgiving than devices.
At the bottom of post #1 in the Harmonia 2 thread (in my sig), is link to how to properly wipe and do an md5 check.
If you do all of this, and you still have a problem, check to see if that rom has a particular bug. If not, then your phone has an issue and needs to be replaced.