Bios password bypass

Sounds like the system board is bad.  

No.  The only way to get past the password if it's unknown is to call Dell, verify your system ownership and obtain a master password for your system.  There is a charge for the call unless the system is under warranty, and you MUST place a voice call - there is no other way.

I have rang dell i put the code in they gave me but it wont accept it ......it wont let me accessany thing once the dell logo has gone off it just brings up the  system or admin code screen

It was working before coz i was loading the windows screen

Did you set the password, or did it suddenly appear?  If the latter, the board has likely failed.  If you set the password, lost it and the code they provided you doesn't work, has the mainboard or service tag been changed at any point in the system's history?

My daughter set the password then forgot it....as far as im aware nothings been changed in the systems history .......all i know is the computer guy who had it before put windows 10 on it

One way or another, if the master password Dell generated fails to unlock the system, the only solution is a replacement mainboard.