200w ? ok first thing you do now screw open your comp and watch what psu you got.. and what kind of comp you have ? proc speed / vid / ram ? so we know how much watts you should have.. but can tell you now 200w is not gonna cut it.. i have like 3 250 watt psu's laying around from age old comps
for pretty new systems ( last 2 years ) i would go for a 350watt + psu at least.
then if your psu is ok i would say its the mobo since your getting problems with anything.. did a error checking on the hd already ? see if it got a large ammount of bad clusters etc.
as you reinstalled 4 times already i doubt its a software problem unless the cd you got is broken ;x
just orderd a new mobo for my bro's comp its giving the ghost blue screens all around ps2 port broke a while ago ( he had to buy a usb mouse ) and now getting problems with blue screens not booting sometimes it doesn't even run as far as the hardware checks.