It's time for a new system. Your board, ram, and power supply are too old to save. Check craigslist or ebay for complete systems, or fatwallet or slickdeals for new system specials in the usa. I won't post individual parts unless you really want to build your own. Lots of old pentium 4 systems locally where I live for $50 and some amd's that are even faster on craigslist.
I agree- it's a ten-year old hand-me-down from my sister, but since it's just for my five-year old to access his reading program on internet so not worth much to upgrade as I'm sure he'll get something new in a few years. Found a used motherboard for $25 on E-Bay which may be the way to go if that's indeed the problem. Then again, the time this is taking me to troubleshoot, it prob won't be long til I follow your advice. Unless I happen on one at a thrift store for a few bucks and want to gamble with it. Thanks.