Unable to enter bios screen

I have a problem with my PC, I am not very PC literate but it is running Windows XP and ASUS MZN-ESLI, it will not go to the windows screen, it just keeps looping between the ASUS screen & a black screen with writing on, I have been told to go to the bios screen by pressing the del key and then press the last option on the top of the screen, which will then get me to Windows. I have tried this but it says it is entering set up but nothing happens and it just loops again HELP, I know I need a new PC but this has all my files for my pub on it

 

Tell us which operating system you are running and what the black screen with writing says.

 

it sounds to me as if a piece of hardware is making it loop
what you need to do is watch the screen when it boots and as it goes through it bios hardware check routine make a note of the last thing it displayed on the screen before it resets and starts again ( loops )

let us know how you get on

 

ASUS is infamous for using faulty capacitors which clobber the voltages used for the CPU and/or memory when they fail. ( http://en.wikipedia.org/wiki/Capacitor_plague )
But; the foremost concern is your data!
With the Power cord unplugged but everything else plugged in, lay the PC on its right side. On almost evey tower, there will be one or two screws on the back edge, after which you slide the side cover back about 1/2 inch and lift it off.
Unplug the power cable from your hard disk drive. (Here is a guide with pictures)
Now, look very carefully for any bad capacitors. If you find them, you now know what's wrong.
If everything looks good, with the power still disconnected from the hard drive, try turning it on and see if the Del key lets you into setup.
I actually hope that it won't as the other cause of your reboots and no BIOS is the hard drive itself failing.
Supply me with a progress report, OK?

 

i think it is
there should be enough information floating around the net to find what the next piece of hardware is checked and making it loop if the motherboard is known

it would be one step closer to finding what going on