I need help with reviving an ancient computer system?

OK so in the 2000 I had this system which had Intel D850 MV mobo, Intel Pentium 4 1.53 GHz processor, 256 mb dd ram, AGP NVIDIA GEFORCE MX 4000 graphics card. Some years later I upgraded and packed my old system in running condition. My sister now needs a computer so I took out the older system but when I try to switch on the older system it refuses to display ANYTHING. The mobos lights are on, the fans are spinning but there is absolutely no output to the monitor. What can be the reason for this? I see no visible damage to the system. The electrolytic caps are not bulging etc. Does a hard disk needs to be connected to older systems to display something to the monitor?