I haven't had or looked at a Compaq laptop for years but that sort of thing is definitely a power management software thing. You will find there are different profiles for different situations for the laptop - it'll be in there, just keep digging.
Actually, the management software might not be installed - hence you not finding it. It could be the only interface to those settings and if you don't have it installed ...
My IBM does it and I can adjust the power profiles however I want - spin down the hard drive after so many seconds of inactivity etc etc ...