Laptop turn soff from sleep mode

[Xgillman]

Hi
i really want this problem sorted out as it is causing me a lot of trouble,
whenever i put the computer onto sleep mode and leave it for a bit, i come back and wake it from sleep ( by pressing the mouse ) and then fans turn on but then it turns off?
Please help
i tried going into bios but cant find the power managment settings
my laptop is a acer aspire 4740G, Windows 7 Home Premium

 

[night wolf]

go to control panel, then system and security.

 

[Xgillman]

Then..

 

[night wolf]

go to power options, (balance) change plan settings. change the power settings there.