Windows is low on memory?

[loudflesh941]

My dad is kinda having problem with his laptop.
He is kinda busy so he asked me to help.
He is getting windows warning that "your computer is low on memory. please turn off these programs: Explorer, Folders"

Since he doesn't even have internet explorer open, I guess it is windows explorer..

I looked at memory usage. It says that 3.2gb / 3.9gb (80%+) is being used. The problem is that he only has like google chrome and couple of words open.
When I look at programs/processes, chrome is using like 100mb, then is like goes down for other processes and if you would add all the processes memory usage up, you wouldn't get more than 300-400mb of memory usage.

Is this some sort of a virus or something?