DamonYoules said:
what you should do is head to the nearest shop that sells the cables and buy both (plus a converter if you need it for the dvi to work). When you get them back home unpackage them very carefull and keep all the packaging and extras etc. Try both the new vga and both the new converters out. If none of it works, then return everything for a full refund (as long as you havent ruined the packaging-check in the shop you can open it without ruining it). If you one combination works then return the rest.
Ive had this issue when the cable hasnt been plugged it properly before, which means normally the cable is broken or a port isnt functioning properly. Could also have been if you did a driver wipe sometime though that is unlikely and normally windows fixes it (though i wouldnt say its reliable).
Hope i have helped in some way.
i have been using the same monitor and cable for my previous comp,it happened in that too,soo i guess its the cables problem.shud i buy a new vga or dvi cable also what the diff between dvi and vga,and shud i buy new monitor