What is the graphic card? What Dell model?
Dimension C521.
NVIDIA GeForce 6150 LE Integrated Graphics GPU
Integrated 7.1 Channel Audio
Integrated 10/100 Ethernet
AMD Athlon™ 64 X2 Dual-Core 4000+
Windows Vista® Home Premium
2GB Dual Channel DDR2 SDRAM at 667MHz- 2DIMMs
320GB Serial ATA Hard Drive (7200RPM) w/DataBurst Cache™

Is it normal to have to turn off and rest your PC after about 4 hours.

Thank you all for replying.