2 short beeps with Dell Dimension 9200

Hi, I was given a Dell Dimension 9200,

I tried to power it on, the computer does power on, however there is nothing on the display, only 2 short beeps.

I tried to switch to different RAMs, and I powered it on without the hard drive and DVDROM, but I am still getting the 2 short beeps.

Does anyone know what is wrong?

Many thanks