Need help with rebuild please

Hello all,

            I am new to this site and am hoping that someone here can help me. I have a 2007 Compaq Presario Sr5130NX that I am trying to upgrade/rebuild. My power supply went first, so I replaced it with a 250watt ATX 115V/60Hz. The computer ran very slow and hung on sites all the time. I wiped the computer and took it back to factory settings and deleted un-necessary programs. It still lagged. I looked into upgrading RAM, so after researching what was compatible I upgraded to 2GB DDR2 per specs. not too long after that the hard drive crashed, so I upgraded to 1tb hard drive per specs and decided to upgrade to windows 7. This is where I ran into my newest problem. Windows 7 loaded without problems, but I was unable to update or load any other software without the computer freezing or converting to a strange screen. I realize that this is probably due to the older CPU. The current CPU is AMD Athlon 64 x 2 3800+ AM2 65 watt. The specs states that I can upgrade to AMD Ahtlon dual core up to 4800+, up to 65 watt. Does this mean I can not go above 4800 and 65 watt. I must admit I don't know all the lingo.
      Sorry for the long post but I would appreciate any help. Also if anyone knows a good place to buy CPU's at a decent price that would help as well.

                                                                                      Thanks,
                                                                                           Babynurse

This is just me, but I wouldn't waste the funds on a new CPU to put on an old motherboard. You've already invested in new RAM, new power supply and new hard drive. The "strange screen" you are referring to is probably a "stop" screen, also known as the "blue screen of death." If you're going to invest in a CPU, then invest in a motherboard as well. You don't have to spend tons of money to get a decent board and CPU. The Windows 7 OS that you are using, is it for a specific brand of PC (restore disk that came with a PC) or is it an OEM...a straight Windows 7 install disk? Not being able to update can also be due to the BIOS system time and date not being correct, and the reason it might not be correct is that the CMOS battery on the motherboard is dead.