hi , I have an older HP pc.I have a new Nvidia video card ,plenty of power and a new hard drive. It still runs SLOW when trying to play games , freezes up or occasionally I get a blue screen . Not sure what to replace next. I guess the bottom line is that it needs to be a gaming compatible pc. Trying to figure out if I need a better processor and if so would it work with an older motherboard ? Any advice is GREATLY appreciated
processor is AMD Athlon x2 dual CORE 5600 + 2.8 Ghz
RAM 2 gb
Video card Ge Force GT 640
Win7 ultimate 64 bit
motherboard micro ATX It is very hard for a home user to verify a motherboard. There are just two many parts that could go bad with no or little visible sign.
Do you know how old the Desktop is? Before 2006, more or less, there is not much you can do to upgrade. After that year some significant changes were MADE in desktop designs. Mostly for better.
"A few of the ready made Desktops were fair game machines with a little work."
- From the comments of others. I don't really know of a  standard desktop was ever a good game machine.

If you have a very modest budget, you might think about  a used console instead of a PC. See if any of your friends will trad you the HP for a console.
Quote from: kathy517 on November 04, 2014, 07:06:12 PM

hi , I have an older HP pc.I have a new Nvidia video card ,plenty of power and a new hard drive. It still runs slow when trying to play games , freezes up or occasionally I get a blue screen . Not sure what to replace next. I guess the bottom line is that it needs to be a gaming compatible pc. Trying to figure out if I need a better processor and if so would it work with an older motherboard ? Any advice is greatly appreciated
processor is AMD Athlon x2 dual core 5600 + 2.8 Ghz
RAM 2 gb
Video card Ge Force GT 640
Win7 ultimate 64 bit
motherboard micro ATX

2GB RAM is not enough for Win7-64bit.
http://windows.microsoft.com/en-us/windows7/products/system-requirements