Need help, computer crashing during game play

Hello All,

I need some serious help. My computer is a little over about 4 years old and I recently had to change my graphics card out. From an ATI to Nvidia shortly after I noticed whenever I play any sort of game that is graphic intense my computer crashes. It used to run fine with the HD 3800 from ATI. Now with my geforce 9600 GT it crashes almost every game every time with the exception of a select few.

I have done burn in test with no crashes. I have upgraded my powersupply from 580 to 700. All my drivers are updated and still get the crashes. I have checked my hard drive for errors. I have no viruses or spyware.

I have also done a who crashed it and I never get any sort of report back. It never gives me a blue screen just goes black and the sound starts skipping.

Any help would be appreciated. My specs:

Computer:
Operating System Microsoft Windows XP Professional
OS Service Pack Service Pack 3
DirectX 4.09.00.0904 (DirectX 9.0c)
Computer Name GODZILLA
User Name Patrick

Motherboard:
CPU Type Intel Pentium III Xeon, 3000 MHz (9 x 333)
Motherboard Name Unknown
Motherboard Chipset Unknown
System Memory 2048 MB
BIOS Type Award Modular (07/25/08)
Communication Port Communications Port (COM1)
Communication Port Communications Port (COM2)
Communication Port LGE Bluetooth TransPort (COM4)
Communication Port Printer Port (LPT1)

Display:
Video Adapter NVIDIA GeForce 9600 GT (512 MB)
Monitor Plug and Play Monitor [NoDB] (613DD1KCA7231)

Multimedia:
Audio Adapter Intel 82801GB ICH7 - High Definition Audio Controller [A-1]

Storage:
IDE Controller Standard Dual Channel PCI IDE Controller
Disk Drive SAMSUNG HD501LJ (465 GB, IDE)
Disk Drive Generic STORAGE DEVICE USB Device
Disk Drive Generic STORAGE DEVICE USB Device
Disk Drive Generic STORAGE DEVICE USB Device
Disk Drive Generic STORAGE DEVICE USB Device
Disk Drive Generic STORAGE DEVICE USB Device
SMART Hard Disks Status OK

Partitions:
C: (NTFS) 476929 MB (343928 MB free)

Input:
Keyboard HID Keyboard Device
Mouse HID-compliant mouse

Network:
Network Adapter Gigabyte GN-WP01GS PCI WLAN Card(Turbo) (192.168.0.105)
Network Adapter PdaNet Broadband Adapter - Packet Scheduler Miniport
Network Adapter Realtek RTL8168C(P)/8111C(P) PCI-E Gigabit Ethernet NIC
Modem LGE Virtual Modem

Games I am experiencing the problems with:
Starcraft 2, Diablo 3, League of Legends

All on low settings or high doesn't matter.