I never had previosly a similar problem!
I just bought a seagate momentus 7200.3 320gb and mounted on an external usb II enclosure.
I was trying to make a partitin backup using the acronis trueimage 2009 software. This did'nt end as expected and created a new partition that I did'nt want.
After a partition removal under windowx xp environment I am not able any more to see the full capacity of the disk, practically the partition was deleted withot freeing the corresponding unallocate space.
Actually the higher capacity I can use is no more 320 gb but only 79GB. The same appears in partition magic 8 and Seatools for DOS.

Seatools reports that native lba is about 600,000,000 while the actual LBA is about 150,000,000

but if I try to restore capacity to native i get the following message
error on SetMaxAddressExt (625142447)
Check to be sure that the drive has been power cycled.
set capacity max native failed

I have not received any seagate support, yet.

Any one here can suggest me something to do in order to recover the full storage.

I don't care data as the disk is empty, just prefer no to ask for a RMA if not really necessary.

if it can help, my configuration:
Dell laptop inspiron 9400, 2gb ram, core 2 duo 7200, sata/USB II encosure Atlantis,

It's clear that I am not an hdd Guru I posted this question just for ask your help
Thanks in advance

SeaTools won't work properly with USB box. Connect the drive to a DESKTOP PC for diagnose. Use MHDD with pure DOS to check (EID) the capacity and look if HPA was not set.

Yeah what BlackST said, with the addition that some of those USB boxes use funky parameters on their drives, and if you format the drive in it, it may not work correctly without some logical modification if put into a computer.