System Memory Decreased-How to increase it?

Hey friends,
When I start my computer , it show "The Firmware has detect that the system memory has decreased" . Press the enter Key to continue .
I don't know but this is quite so unnatural that the systems memory is decreased by itself. Is this done by any virus or any threat is there in my coputr system only.
My question is why this type of message is displayed?

Ensure that your RAM is clean off any dust and then restart your computer. This may happen when there is dust on RAM joints and the RAM memory is not detected by the system. Not a virus or any such kind of threat.