Faulty ST3500320AS Hard Disk

Hey, I received the parts for my new computer, well packaged and working beautifully.. apart from the hard disk.

Yesterday my computer began running badly, lagging a lot and also the hard disk was making a lot of noise whenever doing things on the computer. I then rebooted and windows wouldn't load. I tried booting with last known working settings and that worked but the computer still ran badly.

I ran the Seatools hard disk diagnostic program and it told me my hard disk has errors.

I'm not sure what to do now. I obviously need a replacement, but I'm not sure what the best way is of doing that. I don't want to have to send it off and then wait for days before I can use my computer again. I actually wanted to get a second one of those hard disks anyway.

Could I maybe buy 2 of the hard disks and then send off the faulty one for a refund when they arrive? Would I have to pay for postage? Would it be possible to get them sent faster than normal seeing as it's a replacement?

Thanks for the help, and apart from that the service was great!

Johannes