Despite of the quality of TNT2M64..have u checked
your driver and directX version..?
i used to have a TNT2M64 and it runs fine on my old
K6-3 400mhz..and if u're using via chipset motherboard..
the via 4 in 1 driver(the agp one especially) may coz
the problem too..try to grab the latest one and see wat's
happening..sometimes it's fun

to palying aroung with
those configuration..
IMHO..the tnt2M64 isn't dat bad..one ofmy friend even
enjoy playing with his tnt Vanta..just if u got the setting
optimized for it..

oh btw..u didn't mentioned wat game u're playing..sometimes
the screen just stun right after the loading..press F4 and see..it's
something with the SPU irq dat u gotta turn it on'off via manual