IS that PSU enough for that system?
The long shutdowns can be MANY things, mostly dealing with your XP setup and processes you have installed and or running, and how fast you have some things set in the Registry such as Waittokilltimout And the other timout settings. All of which are very messy it changed wrong. So we will leave those alone for now.
As for your slow startup, AHCI likely is the cause of the hang there. But I would also say memory issues can cause the system to not fully boot as well.
Sadly, I do not know much about AMD, so little that I do not even know if the board you mentioned is new or old! HAHA Really
But I can say that ram is kinda cheap right? Are you sure it is good still? have you tested it with memtest86+ Version 2.01