i have done correct all the prcocess of installing a new SATA hard drive as a slave in a windowXP OPTIPLEX 755 computer but it did not recognize a slave in a computer

There us no such thing as Master/Slave with SATA drives. Master/Slave only applies to PATA drives and even then, it is a hangover from the past. The drives might just as well be called A and B as you can put two drives on the same cable. With SATA each drives has its own dedicated interface on the motherboard. So exactly what did you do?
Stuart
In BIOS are the drives recognised correctly ????
only the original one was recognized
"only the original one was recognized" Well you have determined the problem, the drive has not been recognised, time to read the motherboard manual and ensure the SATA Controller is correctly set !
The confusion comes from the references in the BIOS. While SATA drives do not share bandwidth they DO share controllers. There are usually two SATA ports per SATA controller. So, a SATA drive can be connected as a slave but still runs independently. That is, unless it is configured as part of a RAID setup.
Atu
You may need to enable the SATA controllers in the BIOS screens. Note that SATA drives also require both power and data cables in order to operate.
Watch the POST screens at start up where all the hardware is configured. All your drives should appear by both model number and full drive capacity. If that doesn't happen then they will never work in Windows.
Thanx guys for your replies,am working on it
