i agree with the above that its a hardware issue.
My first thought was it is overheating,
Try taking the side of the case off and may as well leave it off,keeps the system cooler anyhow[i have both sides off permanently]
While the side is off and the system switched off ,use your hoover to clean the processor heat sink and generally clean up any dust thats accumulating in any heat sinks and the PSU
A way to check if its a heat prob,is to swich on -go straight to bios and watch to see if your temperature readings are above what you would expect on a normal boot up[say 30-40c]if its running hotter [say it starts to climb to bout 60-70c then theres your prob and best put a new one together,also check to see if the temp warnings alarms are switched on.
Amd chips run much hotter than P4 chips
,Ive had some running at 160c briefly
before it melted[an old system on its last legs]
I found it would boot OK ,run awhile,then crash .If i tried to boot up straight away it would continue to crash a few seconds after booting up
It was only after i left it for 1/2H would it boot up to desktop,i could then run some things ,but an hour or so in ,down it goes
Buy a new system[they arent that much these days
or you should be quite able to pick up all 2004-5 stuff that you need for well under £200[well under as you already have a copy of windows] ,so that's 1 less item to add to the new build and most wee shops are quite happy to use your disc,and put the system together for you
1976 Raleigh Chipper,1991 Muddy Fox Adventurer,1991 Claud Butler Ventoux 400 ,1992 Raleigh Diablo ,1992 Rudy Project, 1995 Cannondale M200 ,1997 Santa Cruz Tazmon ,1997 Specialized Stumpjumper ,1997 Specialized Rockhopper ,1997 Marin Quake 9.0,1998 Marin Pallisade trail ,1998 Raleigh Torus,1999 Orange Clockwork , 2005 Kona Hahanna ,2007 On-One Inbred ,2010 Orange Pure7 And of course The Ti
The Marvellous Mechanical Hope Collection ,and other Hope niceties