Laptop sometimes logs off on opening lid

My main PC uses XP, but I look after some Windows 7 laptops for a charity.

The laptops each have an admin user and an ordinary user. On one of these laptops when we close the lid in an active session and re-open the lid, it shows a screen to enter a password. About 50% of the time we can just enter the password and carry on. Nothing new there.

However the other 50% of the time the laptop, either immediately or just after we have entered the password and it has shown us the open windows, logs off without any warnings. There are no messages and I cannot understand why. We have taken to making sure we leave no significant windows open, else work can get lost. We have never had a laptop log off unprompted at any other time.

The laptops are HP Compaq Presario CQ61, and do not have much more software on them than MS Office, IrfanView, Foxit, Family Tree Maker and browsers.

Thanks for any ideas.

 

Click the battery icon in the right bottom tray and click on adjust screen brightness. On the left side, click the "Choose when to turn off the display ".
Now the third option is put the computer to sleep. There is a drop down menu with it which starts with 1 minute and end with Never.

Select it to Never if it is not already selected and you wont face this problem again hopefully.