How to select 1 of 2 win 7 installations

Hello all,
I have an older computer with a SATA drive and an old PATA drive. Each drive has a Windows 7 system on it. When I boot up the machine, it defaults to loading the system on the PATA drive and not the one on the SATA drive because the PATA system is a newer installation. I recently added that hard drive to the machine.
I do not want the PATA drive system loaded at boot. I want the computer to default to loading the Win 7 system on the SATA drive.
How can I change the machine to boot from the SATA drive and not the PATA?
The machine is old and the BIOS is old. There is no option in the BIOS to change boot drives. The only option is to set the “Hard Drive” to boot after the CD does. It does not differentiate between SATA and PATA.
I have tried numerous boot discs with no luck. Windows 7 does not have this option either.
Can someone please help.
Thank you.

Normally, you can select BOOT MENU.

If no boot menu, go into BIOS, under the option of “Hard Drive”, it should list all hard Drives, say WD 500GB. HITACHI 320GB, , ,

Then you can move the order, which one/disk boot 1st. which one boot 2nd, , ,

Even old PC, this option is usually offered.

siliconbeaver said:

Normally, you can select BOOT MENU.If no boot menu, go into BIOS, under the option of “Hard Drive”, it should list all hard Drives, say WD 500GB. HITACHI 320GB, , ,Then you can move the order, which one/disk boot 1st. which one boot 2nd, , ,Even old PC, this option is usually offered.

Thank you Silicon!
I had misread the line item in the BIOS to change the hard drive boot priority. I thought the line item description was the TITLE for the items in the column below. In fact, it was indeed the alternative to change hard drive boot priority. Your reply made me look closer. I have just changed the boot priority to the SATA drive. All is good!
THANK YOU AGAIN!