There are still lots of LGA775 board available in the market. You should be OK. Both your CPU and motherboard are rather old and a new machine would do you wonders especially with the new i7 block of processors and the faster performance of new gneration DDR3.
I agree with Vegan. That motherboard is End of Interactive Support and End Of Life. You can get better performance and maybe even cheaper than troubleshoot this problem.
Still if you want to troubleshoot it here is a useful guide with the basics: