why has my monitor vertical lines on it ?

[redindian40]

Intel Pentium III mobo
Intel Pentium III 650mhz processor
320 mb ram
GeForce Ti4600 graphics card
internal PCI modem
30gb hard drive
cd rom drive
Flopy drive
midi tower case

i recently bought this cheap base unit for my son from the
hardware classifieds forum and on connecting up the unit
to a monitor with a dvi - vga adapter all the monitor is
showing is vertical coloured lines nothing else can anyone
explain what the problem is as its also doing the exact same
on a 2nd monitor that i have tried it with both monitors are
working fine with other units can anyone help me with this
please

[lisag]

Do you have another graphics card that you could try in it?