Opinions please?

I recently pulled apart my old system that had been sitting there for 6 months (it had a problem I couldn't troubleshoot so I didn't bother with it, kinda took a break from computers) when I first tried to turn it back on I was getting no power at all, so I went out and bought a cheap case (the old case was pretty crap and REALLY dirty) and a new power supply (Antec Neo Eco 520c) to renew its power. I wanted to rebuild it because I wanted to learn how to do it so that when I go out and spend 2000+ on a brand new system I can be confident I can build it properly.

Anyway, I did my research and eventually ended up connecting up everything (yay) and successfully powering up the computer on the first go. However, it loads past the BIOS then when it should get to the Windows 7 loading logo screen it doesn't, and just stays black. There are 3 beeps on startup, which with research seems to indicate a problem with RAM. I took out the four sticks of Kingston 1GB DDR that were in there and tried them all individually, with the same results. Other people said it could have something to do with my video card, but without another one lying around I can't really test that. I took off the chipset/southbridge heatsink and lost one of the spring plugs trying to reconnect it, so I left it off because again with research people didn't seem to think it was necessary for a southbridge unless overclocking. Will the computer detect no heatsink and not start up? I should mention that all the parts in this computer are several years old (320gb Maxtor/Seagate HDD's, AMD Athlon 64XP I think, etc.) and were very unclean due to sitting idle for so long. I also tried unplugging various HDD's, but no avail either. SATA HDD's automatically detect which drive has windows on it yea?

Anyway, I think maybe that because the parts are so old and had been so dusty and dirty, that some part(s) is not working. I guess what I'm asking is for any tips to troubleshoot the 3 beeps problem, as I was going to give it to a family member if I could get it working, but don't want to have to buy several additional new parts costing a few hundred, or should I just scrap it and buy parts for my new system?

Sorry for the wall of text, but this has been doing my head in! Any advice would be greatly appreciated

If you had the motherboard owners guide you could find out what the three beeps means. The motherboard bios checks for certian pieses of hardware , cpu , vga card , and ram. Any one of those things that are not detcted there are a sequence of beeps associated with it to let you know what is missing. The motherboard user guide has that sequence listed in the section that detailes the first start up. At the point you are at if you go any further you will end up buying a new computer , so maybe it's a good idea to call it a day and move on.