It's possible that the PSU has blown.
I've fallen foul of the "obvious" (video card).
the power unit delivers a number of feeds at 12 and 5 v
and if the regulator blows you will get the correct voltage .... but at (almost) zero crrent.
ideally you need access to spares to prove what the problem is
if not .... guessing could be expensive
your options are
Maplins sell a psu tester
http://www.maplin.co.uk/Module.aspx?ModuleNo=4 5500&C=Froogle&U=45500&T=Alias&MA=PSU%20Tester
they also sell PSUs
and video cards
(but they are neither the best nor cheapest)
almost any PC PSU will do to prove the fault .... but you want to buy a reasonable unit
(250-300 watt - �20-�30)
then there is the video card? onboard graphics
the options there are new mobo (onboard)
or if onboard or seperate. a new card
4.5 years old .... don't get silly it's not worth it 128Mb max
my money is with matt1e .... sort of ......
not sure I follow the memorystick thing though.