Hi. I need some help. My 2 and a half years old Mac Pro 8 cores with OS X 10.5 was running quite slowly and re-booted randomly, so I decided to reset the PMU by pressing that little grey button on the mainboard. For a week or two, everything was fine, but today suddenly I noticed that the machine was slow at startup and just couldn´t login with my user account: after entering my password, a blue screen appeared and I heard the disks working, but then returned to the username/password screen. I tried to use the guest user account and other account with administrator privileges, and they worked for a few minutes, although the machine was slow and finally it froze down. I was able to move the cursor around the screen, but nothing else. Are the PMU problem and this issue related or it´s just a coincidence? I managed to check the start-up disk with the disk utility , and it said it was OK. I tried to startup in safe mode and it didn´t help. What else can I do? Run the hardware test with the OS disc? Fresh OS reinstall?----> And if I do a fresh reinstall of the OS, am I going to keep everything I have in the other non-system disks which I run in a RAID 0 setup? Thanks a lot for your answers.