Some monitors will not show anything at certain resolutions, so use a better monitor to set the resolution form the computer software and if that does not work then you may have to get another or repair the the one you have
now you will have to weigh the pros and cons about repairing...
pro---repair will be cheaper
con-- it has been repaired--don't know how good the repair will be, don't know if other things are going bad with the monitor- don't know how expensive it will be......
if the repair is less than $ 40.00 you may want to do it or buy a used monitor for the same price or a little more.
or you take the that money and put a little more and buy a brand new monitor
here in NY you can get a brand new monitor for around $135.00
hope this helps
steve