i have installed a 2nd HD for storage and it only shows 127g , not 500g ?? it does show 500gb in the bios section but properties only 127gb. 1st drive is Tb on the sata 1, 500gb is on sata 2. i am using a m3n78 pro asus MB!
Go to Disk Managment and see if there is any unallocated space. Try deleting the existing partition, then create a new one in Disk Managment. If using XP, Service pack 1 or later is required to enable 127GB+ drives. Bios needs to be set to Auto LBA.
Did the 500GB HDD arrive in a factory sealed antistatic bag?
If the seal was broken maybe you got a returned drive that some one partitioned and formatted on a system and/or OS that didn't handle 48-bit LBA.