problem with graphics! GeForce FX 5500

[nozikins]

This happens after about 30 minutes of playing Ragnarok online... the text in chat, stats and item description get garbled

text graphics garbled

another messed up screen

Already did:
- updated video driver
- got latest Direct X
- lower hardware acelleration - put it back up to highest
- checked graphics card capacitors -

My PC is 1 year old but just got the hard drive, power supply, and graphics card replaced by computer shop since it was defective and still under warranty.
Processor AMD Sempron 2400 / AMD Athlon(TM) 1500+
Motherboard ASUS A7V600-X
Memory 512MB DDRAM
Hard disk Seagate 80G (2 pcs)
Monitor 17" Boka
Video Card NVIDIA GeForce FX 5500 256 128bit
screen resolution 1024 by 768 32 bit
Direct X9

Also experience problem when playing Warcraft the screen freezes after 30-1 hour of playing, I can still toggle the controls since I can hear the sounds, but the screen is either frozen or black.

HELP! Should I go back to the shop and get the graphics card checked? Or should I just get a new better card?