7 yrs is ancient in the electronics/computer world! All your connections need to be cleaned... power supply cables need to be taken out and reseated. any cards you have need to be taken out and the gold contacts need to be cleaned with a pencil eraser. most importantly, your RAM sticks need to be taken out, cleaned and reseated. wear a ground strap too when your doing this.
i hope this helps but if not, it is the logical first step!