Rooker

It splitted in two equal parts, both NTFS, When i tried to use it as a single logical disk, the system shows only 128 Gb

I'm using: Athlon 64, MB: Epox nForce 3. everything was just perfect till the day i decide to change my second HDD, it is Seagate Barracuda 200 Gb after i plug it in and run win 2k something goes wrong! when i tried to erase something from this new HDD or launch something i recieve an error message. I've checked it with CHDSK and it found a LOT of "wrong indexes" At the same time the first HDD (it is Baracuda too but 60 Gb) works perfect no mistakes no errors. When i test this HDD (a big one) on my neighbor's PC, nothing happened there was Athlon 64 too but it works under win 2003. What's wrong? Hope you'll understand what i'm trying to tell