I could use some advice on building my computer to a functional status.

[tech3149]

I've built my own machines since the 80's and my career has always been in the dirty end of electronics. I'm not a computer geek and have pretty much no interest in software, I just try to live with it.
The last machine I built was what I thought was the best I could get for my money. As we all know, that's a pretty serious consideration.
The original machine was built around an Asus P5KPL MB with a 2.2G Intel Dual Core processor, Geforce video, DDR2 ram. The drive is a WD 500G SATA.

I got nailed by a lightning strike and paid someone else to get it back into working condition.
First problem, he couldn't save anything from the HD (even though I was able to read the HD and copy most of the important directories)and had to reformat and reinstall all the basics. Second he trashed my old but useable video card when the only problem was a few questionable capacitors.
Replacing the video card meant a new PS that could support the Radeon 5700. That's all well and good so long as it lasts as long as the original machine.
Well that didn't happen. I have had consistent problems with freez ups, inability to reboot, mouse being unresponsive on reboot (Logitech wireless mouse and keyboard).
I'm still running XP SP3 because it plays well with some of my older simulation programs.

When this guy rebuilt it he installed Avast free version software, I had been using Avira for years with no problem.
Besides the boot and reboot problems when browsers would just hang. When I first started noticing the problem I watched the resource being used by what processes. Avast was the dominant resource hog. Add to that that it was constantly reporting MBR infections but could never isolate or delete them.
I went back to Avira and things were much better for a week or so. Before that I went from Firefox to Avant to see if would make a difference. Avant worked better over both antivirus app's.

My major problem is the cost of memory especially but processors and MB's are much higher than they used to be.
I'd like to use what is most likely more than functional and minimize spending money on things I don't need.
First suspect the MB. I've been using Asus MB's since my second build and they have always been reliable. Prior to that I used FIC. Is there a better option, does it really make any difference?
Is DDR2 useable on a MB designed for DDR3? Can I still find a MB that will work with a Dual Core?

Sorry for the long rant but I know if anyone can offer suggestion it will be here.
If you took the time to read this I offer my thanks even if you don't have any advice.

[hobbit709]

1. sounds like there are several problems.

1. DDR2 is not compatible with DDR3.
2. Is it a socket 478 or 775 processor? If it's 478, forget it those are hard to find. A socket 775 mb that would work with your cpu is probably still available-try newegg.com or geeks.com.
3. It's possible that your hard drive has gone flaky.
4. The problem with a wireless mouse and keyboard is that they won't work until Windows loads so you can't use them to get into BIOS and check all your settings.

[Mnpaul]

2. I would suspect the memory

That is the first place to look. Download something like Memtest86+. Memory prices aren't that bad right now DDR2 is somewhat higher than DD3 but both are quite cheap.

I've used Avast for years with no lockup problems. It sounds like a hardware problem.

[HopeHoops]

3. On a whim - replace the power supply (I'll assume you have others).

It sounds like you aren't getting the necessary output from the PS. If it's an XP device, the things should be regularly available in the neighbors' trash heaps.