A failed CMOS battery. Talk with those that you get support from about replacing that battery.
Ok, so I've got a 4 year old 5536g running Windows 7 and suddenly it won't power up except if I remove battery and power lead for 30 seconds and then replace. Additionally, the volume and wireless etc buttons above the keyboard won't work and the laptop time and date keep resetting to some time in 2009 every time I power it up. Recently I had to break the user password because the user forgot their password, I used Windows Change Password / Registry Editor / Boot CD by Petter Nordahl-Hagen, this may explain some of the problems. Am I way off the mark in thinking I need a new battery and a registry fix after this password boot break?