cannot add new hardware in windows xp pro

[jassu]

hiiii,
if ne1 can help me plzz do mail me.i have a problem
in windows xp pro that whenever i try to install any new
hardware it gives me the following error:
"cannot run two device installations
you can only install only one device at a time
another device installation is underway, when it is
finished you can try the wizard again"

plzzzz help me coz i cannot install ne kind of hardware
onto my system.