Vista Brightness control stops working after resuming from sleep

I am using HP laptop dv6703. When windows vista(home premium) resumes after

sleep, Its brightness control stops working. It does not changes either with

keyboard shortcuts or from brightness control settings in power options, so

to change brightness again, I have to restart laptop again, then it works

fine (i.e changes with options with keyboard shortcuts and power options). Is

their any hotfix to fix this problem please help

thank you