asus machines crashing help

AMD ATHLON 1900XP+ Asus A7n266, 256MB Kingston DDR 30GB Ultra DMA 7200 maxtor, 64 meg Nvidia GeForce 4400 mx Graphics 300 watt psu
I have 2 machines both The same speck they both run o.k. until it comes to games then they both crash I’m talking about games that say they need a 700(+) MHz Intel Pentium III or AMD Athlon processor 128(+) MB of RAM 16 meg video card. I have tried various things to fix this problem i.e. format and reinstall update drivers replace memory, remove processor and reapply cooling paste, replace the fan on the processor. I also tried running win98 se instead of windows xp. I replaced the video with a geforce 4400 mx (64 meg). I put a known good psu in All no joy. Any suggestions??

 

amd xps ussaly req 350w minimum to run stable