Dual Monitors - Inspiron 530

I apologise if this topic has been covered elsewhere, however I am now at the point of tearing my hair out trying to figure this out!! I have a Dell Inspiron 530 that I purchased in 2008. I have made absolutely no changes to it other than upgrading the Operating System first from Vista to Windows 7, and most recently (December 2013), from Windows 7 to Windows 8.1. I have just purchased 2 LG 22EN33 monitors, my Desktop tower has two blue VGA ports at the back, and I perhaps naively thought that using the plug & play functionality would work, and I could just plug them in the job is a good one. However, what I am finding is that only 1 monitor is actually working properly. When I start the computer I get a message about an invalid video card configuration. But no matter what I try to configure it nothing seems to work. If anyone has any advice or suggestions I would really appreciate it!!