More PC dramas

After having built my new PC almost entirely from bits bought from eBay, I have encountered a couple of problems. Firstly my monitor (bought some time ago) started to play up, then the PC kept showing a 'Windows has recovered from a critical error' message (which is NOT encouraging..), so I did a Windows 'repair'. After my repair, I noticed my AGP graphics card was not working properly - that, and the monitor being on the blink makes for an odd combined experience. So I bought a new monitor (well a 'previously enjoyed' one anyway) from eBay (again!) and that was two problems fixed, but the graphics card refused to work as the high-end card that it should be. I tried borrowing another card and putting into my AGP slot, but that one worked no better indicating that maybe I have a problem with the Motherboard.
I ended up buying a new Mobo (from eBay - no surprise..) and am waiting for it to arrive now - I am hoping that I can seamlessly replace the old board, but am not silly enough to be confident that I won't have to start from scratch again with a new installation of the Operating System...
I really really need to try and get rid of my growing collection of Mobos, CPU's CD drives and power supplies - eBay calls again, this time to actually make some money and clear some attic-space..