hard drive + dell pc problem!

Sounds like you are trying to boot off the old HD with your new machine ?
You probably won't be able to do that because of different motherboard, drivers, etc.....
is it guaranteed its gonna work with it>?

I've used this method many a time with success every single time (slave on another pc).
The reason you cant use it on new pc as the boot sector will be different and it will be expecting different hardware. Other than that, the rest of your data will be readable ( I should think).
Just make sure you set it up right for slave use, using connectors according to manufacturers diagram,
If you have access to another pc, try downloading the discprep tool and use the tools to strip out the drivers and force a reconfig. I think once yo uboot from the floppy its diskprep /pnp to force the re-enumeration. Might work.
Just put into the pc a ide cable that has 3 ide plugs, set the hard drive up as slave with the jumper setting on the drive and plug it in, go inot the bios and hit arto detect and save then boot windows back up, you can then copy all the data you whant over to the master drive then take the slave out or do a formatt of the slave in windows and use it.

If you take it out go back in the bios and do again a arto detect so it sees the master drive again.

Have Fun.
If you look at the drive where the cable goes in, there should be a small plastic lug sitting over two pins (usually Master).

You need either a small pair of tweezers or use ur nails if u got any? to pull the plastic bit off and move it along. If you look closely, there are markings written above the pins (MS, CS, SL) Master, Cable Select, Slave.

Plug the other end into a spare ide port on your mobo and reboot and you should see it as a D: drive.
If you don't see the drive under SL, try CS.