Disk Warrior + SuperDuper
A program to scan for bad sectors.
Replacing the twin 2600s.
A clean install and careful update.
USB cables and devices as well as any printer drivers etc.
The ideal RAM configuration is 8 DIMMs though may not be of enough value but that model is different in that setup.
I find too often that Disk Utility was not enough, and that there can be problems that are missed.
Clone the system, repair w/ DU and DW, then test and troubleshoot. Create a new user account to see if that helps.
Freezon system and hard restarts have generally not been something that even a safe restart would fix, as much as it is suppose to clean up and check the directory.