Seagate 300GB SATA

Installed XP on it, and the motherboard won't see over 128GB. So I install Partition Magic, delete the extra partition and create a new one so it's back up to 300. Next it asks me to reboot so I do. It asks me to insert the setup disc so I do. And wtf do I know... It boots from the disc and installs!

So with the new XP on, I put on Partition Magic again but now C: is being read as 128GB and that's it!

How do I get the 300 back???

:wtc: