I'm afraid you will have to bear with me as i am far from an expert. I have just been attempting to install a second hard drive and i am having serious problems, so i thought i'd come here for some help, hope that's ok.

I have installed a hard drive before but this time it just doesn't seem to be working. I have a 160gb western digital drive in already, and seeing as my old 2nd drive packed in a while ago i decided to pick up a new drive when i was in New York (is this going to cause any kind of compatibility issue?) last week. I bought a 160gb seagate barracuda.

Last time i tried to do this i was having problems with the jumpers etc, but managed to sort it out. However this time i just can't seem to get them going. The WD drive has 5 pairs of cable jumpers, and the seagate drive has just 4 pairs. I am starting to worry i have bought the wrong kind of drive.

I have been trying to set my old drive as master and the new one as slave. When i start up the computer it gets to "detecting drives" and then just stays in that screen until i turn it off.

If you need any more information (which i'm sure you will) then just ask.

Have you tried setting them both to "cable select"?

Things to check:
are they both on the same cable? If so, one may need to have the appropriate jumper setting to be a Master and the other the Slave. I've had CableSelect problems before and always try to set Master or Slave now. As they're different manufacturers the position of the jumpers may be different, there's usually a little sticker somewhere on it to assist.
If you go to the manufacturer's website they often have pretty good online installation guides.

When i start up the computer it gets to "detecting drives"

Excuse me for asking the obvious but is this after you've been into bios and told it to detect new drives or is it when you've powered the machine up without going into bios first?

Having just re-read orig post, here's some extra:
Drive bought in US shouldn't cause any problems I don't think
Are there any CD/DVD drives in this setup? They will also have Master/Slave jumpers you need to take into account.

http://www.seagate.com/support/disc/iguides/ata/cuda7200ig.pdf

I suspect your new drive is one of the ones shown in the PDF above. It gives a good image of the jumpers that may assist- looks like you want to have NO jumper on it I think (if you want it as a Slave on the same cable as your WD Master)

Thanks for the replies, i have the western digital drive as master and the new one set as slave.

I don't get a chance to get into bios is just stops on that screen before i can get into it. It doesn't crash, it just stays on detecting. Has really been puzzling me.

Which, assuming the jumpers are set correctly, would suggest that your new drive is dodgy in some way...

Try just attaching the new drive to your PC, & see what happens. But before you do that, go into the BIOS & make sure all the hard drive settings are set to auto-detect.