Replace Primary Master Hard Disk with Primary Slave

I have a desktop computer with following specs :
2.93 gigahertz Intel Core2 Duo
Board: ASUSTeK P5QPL-AM Rev X.0x
266 megahertz
BIOS: American Megatrends Inc. 0408
Intel(R) ICH7 Family Ultra ATA Storage Controllers – 27DF
Intel(R) N10/ICH7 Family Serial ATA Storage Controller – 27C0
Primary IDE Channel [Controller] (2x)
Secondary IDE Channel [Controller] (2x)

I recently purchased a 160 gig HD and used it as the Slave disk. I formatted it and installed Windows XP while booting from and using the windows XP on the old disk. Then I removed the primary master (Old HD) and used its power and data connectors on the new HD. However, the computer does not boot and asks for a boot media.

If I read your tale correctly, you now have only ONE IDE HDD connected to the Primary IDE port. Any IDE port MUST have a Master device, and MAY have a second device as Slave. There are two options for designating the single HDD as the port’s Master. The most straightforward is to set the jumpers on it to the Master position. Use the diagram on this drive to guide you, NOT the diagram from another drive. Then connect this drive to the END connector on the ribbon cable if at all possible.

The other option is to set the drive’s jumpers to CS (for Cable Select) and then the drive MUST be on the END connector in order to serve as Master.