Invalid system disk error

I'm running a Dell Studio XPS 8100 with Win 7.
Every now and then when I boot up I get an Invalid system Disk error. Remove the disk and press any key to continue. Since I have no other disk in any of the drives I press any key and the boot goes on as normal.
I used to get this on some of my older machines when I would leave a disk in the floppy drive. Any ideas?

If you have an USB Pen, Memory Card, or an iPod, for example, the computer mays report that same issue/problem or similar.
Was anything connect to PC at the time?

canongrip wrote in post #11551488
If you have an USB Pen, Memory Card, or an iPod, for example, the computer mays report that same issue/problem or similar.
Was anything connect to PC at the time?

Two external hard drives. That maybe the problem. They are connected through a usb port.

If you're comfortable and aware of the risks, take a look at your BIOS.
Look for boot order and disable/remove USB something..

canongrip wrote in post #11553140
If you're comfortable and aware of the risks, take a look at your BIOS.
Look for boot order and disable/remove USB something..

I've done that before on other computers. Thanks for your help I appreciate it.