You need to disable sleep mode on your computer, most commonly to deal with an error message you saw in CAD.
1. Open the Windows Start menu and type Sleep in the search box.
Select the Change when the PC sleeps option from the menu.
2. To disable sleep mode, select Never from the Sleep menu.
You can also try using this menu to simply increase the time before your computer goes to sleep. However, you may need to select the Never option to deal with the CAD error you're seeing.