Hibernate on Vistas doesnt work

I have been recently experiencing a problem with Hibernate on my Hp computer
(slimline s7520n). Until last week, hibernate worked fine. However, after
installing the Vistas updates that were released last week, hibernate does
not seem to work. When I hit hibernate the machine does not completely power
down. The power indicator light on the CPU unit does not go off. When I
try to restart, it wont. I have to acutally hold down the power button and
force a shut down and restart. At restart of course I get the usual f8
screen - do you want to start normally or on safe mode, etc?

Does anyone have any idea why this is happening now? Does it have to do
with a recent update from Windows?

I look forward to your help.

Thanks

Paippalada