That is a lot of machine, though I am not sure you know exactly what it is
... 500MB RAM ...
Is that accurate? All guesstimates need to be stated as such for accurate analysis, failure to do so indicates lack of understanding. But to what extent also needs to be understood.

Well, the activity light in front is on all the time.
What is meant by this ???

Is it the hard drive light? Or is it an ethernet connection?

If it is the hard drive light, it could be a hard drive problem, a software problem, or include the below.

If it is an ethernet connection light, it could be a software problem, indication that the box has been rooted, is being used as a remote bot, a proxy, a spammer, etc., or normal activity ..... my cable connection receives constant incoming connection requests, scans, broadcasts, etc.

If it has been rooted ....... reformat, reinstall, period.

If not, post the logs ( which you haven't to this point ) and maybe someone could actually help.