Mac Pro 5.1 running very slow after fresh install I inherited a Mac Pro 5.1.

I originally planned to use ubuntu on it. Which I did.

But I am now trying to get back to Mac OS X. Have installed the OS from the provided DVD. However it runs horribly slow. The boot would take 10 min. Every single click takes 30 sec to process.

I feel like I have messed up something at the Apple hardware level. Fair enough, I think I deleted the recovery partition, and messed with boot partition for ubuntu to work.

Question: is there any way to check the basics at the hardware level?
  I have ran disk utility and disk check, nothing there improves. So I am thinking more MBR/Bios/etc.

Cheers
After quite a bit of troubleshooting, I replaced the HDD with a new one. Works like a charm.