Need a new motherboard and case, HELP.

Hey guys, I have a huge proble so any help would be greatly appreciated.

I have a Gateway FX-510 desktop that’s not working.

Last week I was gaming and the display suddenly shut off, so I restarted my computer and it seemed okay, but the next day it happened again followed by a series of beeps. So, I restarted my computer thinking that some weird anomaly crashed my computer.

However, when I restarted the computer this time, the monitor didn’t display anything at all. So I opened up the case thinking that my video card burnt out, and swapped out the defective part for a new Nvidia GTX 460 , but it still didn’t show anything on the monitor when I booted up the PC.

I then called up a local repair center and they told me that either my monitor burnt out, or the defective video card might have burnt out something on the motherboard and that’s why it’s not displaying anything on the monitor.

I’m going to swap out the monitor with one that I know works, however, if it is the motherboard I’m not sure what I can use to replace it, or for that matter, which one I should buy (that’s where I need your help).

If it is the motherboard, which should I purchase? I have a budget of roughly 100-150 USD, so can anyone recommend anything? Please keep in mind that I’m disabled and am currently living on disability till I get a job. Thanks in advance.

Specs:

Gateway FX-510 Desktop:
http://support.gateway.com/s//MOTH [...] 54nv.shtml

Motherboard:
Intel Lavacot 975x (Case BTX, I think... is that worth keeping or just upgrade to ATX?)

BIOS: ACPI 2.0, WFM 2.0, SMBIOS 2.3, USB FDD Boot Support

Chipset: Intel 975x chipset consisting of:
MCH Northbridge Intel D975x (GD-DG)
ICH Southbridge 82801GH (ICH7-DH)

Processor: Intel Core 2 Duo E7xxx series
LGA 775 Socket
1066 Mhz Bus

Memory: Four DDR2 Dual Inline mem Module
667 Mhz (expandable to 8Gb)

Video: MSI Nvidia GTX 460

Audio: Intel High Definition Audio Subsytem
8-channel (7.1) audio with five analog audio output and one S/PDIF optical digital audio output using Sigmatel STAC9220 audio codec

Card Slots: One PCI Express x16
One PCI Express x4 (x16 connector to accommodate video cards )
Two PCI Conventional

Rear Panel Ports: PS2 keyboard Port
PS2 Mouse port
Four USB 2.0 ports
One IEEE-1394a Connector
One Serial port
One Parallel Port
One coaxial S/PDIF (RCA) line out jack
One RJ-45 LAN port
Five analog audio Jacks
One S/PDIF Optical Digital Audio Jack

Peripherals: Two IEEE-1394a Headers
Four Serial ATA Interfaces (300 Mb/s)
One Parallel ATA IDE Interface with UDMA 33, ATA 66.100 support
One Floppy disk drive interface

Security support: BIOS Recovery
Trusted Platform Module (TPM)
Chasis Intrusion

Now I know I have an outdated CPU, but I can’t afford to update everything, all I want to do at this point is buy something that will get me up and running with some room to overclock and/or replace the CPU later on (when I have money). This also includes Memory (since I have DDR2 533 vs DDR3, but I would like to upgrade to either 667 or 800 later on).

I also noticed that Tom’s Hardware listed something like the Pentium II E6800 is the best LGA 775 CPU for gamming, is this true (Can’t paste the link cause accidentally quit the browser while I was typing this up)? What would be the “best” LGA 775 CPU for gamming? Lastly can someone tell me what the northbridge and southbridge do, cause I’ve tried to look for motherboards on Newegg, and they have so many that I’m confused as this point?