I doubt any of your active software, AutoCAD or MSOffice or Photoshop etc., are the reason your system is shutting down due to system memory issues. If it was working Friday it should be working today.
Do you have an I.T. person to talk to? Or are you a standalone one-man shop?
System details?
How much free Harddisk space do you have?
What size Windows Swap file are you using?
Windows OS? 32bit or 64bit?
What changed on your system over the weekend? Something did, "nothing" is not correct.
See if any of these are of help as well: