A friend of mine asked me to install a new operating system on his computer, but it was a bit tricky at first, because when you boot the pc will not let you go to the bios.
The solution, removed the keyboard before booting the computer will ask to rectify the error by pressing the del key, this will allow access to the bios where you can change the boot sequence.
1st - DVD drive
2sd - USB
3td - HDD drive
Why dvd drive first, because it lets you boot from the dvd to repair or install windows or try a linux live cd.