not displaying the objects on icons

ear all
i am facing a typical problem with my win2k server, that is
“objects on icon are not seen” or letters on buttons are not seen
for example
letters on start button such as “start” is not appearing only blank button can see.it is happing on lables i open, after restarting the machine every thing is o.k.
my machine is compaq ml330g3 xeon 2.5ghz server with 512mb ram and plenty of harddisk
with win2k server running oracle 91 as database and vb is fronend.
kindly help
regards
shrinivas