I need to formatting of my PC due to virus attack but when I'm entering the setup, I unable to select the boot device priority. Both HDD & CD/DVD ROM selected at the same time. Therefore I got trouble to boot from CD.
Help me out.

You will need an expert technician for best result.

When entering BIOS, look for Reset BIOS/System Defaults and apply if you can

Can you get into windows?

If you have bootable CD in drive, can you boot to it?

Try to reset defaults first

What operating system you're running, and its version.

Any errors come up when booting?

Any changes that either happened or that you perhaps made to your computer around the time that the problem started; particularly any software or hardware that you installed or setup.

When entering BIOS, look for Reset BIOS/System Defaults and apply if you can

Can you get into windows?

If you have bootable CD in drive, can you boot to it?

Try to reset defaults first

What operating system you're running, and its version.

Any errors come up when booting?

Any changes that either happened or that you perhaps made to your computer around the time that the problem started; particularly any software or hardware that you installed or setup.

Thanks for all sir, I've reset to default & its all right.