uhm... I think we're going in circles here, throwing solutions without diagnosing the problem...    Let's start from the beginning....    1) Unplug all hard drives, optic drives, etc.. both the data cables (IDE or SATA) and the power cables (AT or ATX)  2) Plug the data cable (if you have more than one data cable slot in your mother board use the first one, the one with the lower number, that's the primary) and the power cable to the 160 GB hard drive, if the hard drive has jumpers, set it to master  3) Turn on your computer hit DEL key to enter BIOS:    4) does the BIOS recognizes the hard drive?  does it recognizes it as the primary master drive?  If so let it boot, at this point if the 160 hard drive has a bootable sector (a OS installed) from another machine, it will probably won't get to the windows logo screen before it reboots...    5) Now set your 80 GB hard drive (the one that works and boots fine) as primary master and add the 160 GB hard drive as the primary slave drive, repeat steps 3 and 4...    If BIOS recognizes both drives, it boots up with the 80 GB one and Windows recognizes the 160 GB then you need to safeguard whatever important you got in the 160 GB, set it up as a master again and boot from an installation media format and do a clean OS install in that drive....    If BIOS isn't recognizing your drive, that's what needs to be adressed first, there are times when BIOS doesn't like a particular combination of drives in a particular position, that's why I told you to unplug every drive to isolate the problem.    If BIOS is recognizing but Windows isn't, it could be many things...    Let me know how it goes...