Unpredictable: disabled motherboard features, crashes

Hello,
very grateful for suggestions on the following:
I have had a number of problems for some time which I think may be caused by the same thing. The problems probably relate to the motherboard. The symptoms seem to happen randomly, sometimes one thing, sometimes another:

on start up
no beep, monitor receives no signal
message saying bios corrupt, won't go further
message saying floppy contains a non-system disk (when it is in fact empty)

if start up is successful
screen freezes, needs to be restarted (when loading Windows or during Windows operation)

If Windows freezes during operation, it is often immediately preceded by the on-board Realtek sound card reporting a jack has been unplugged. Internet connection is also cut (ADSL modem via on-board network adaptor)

Also, most USBs (on-board, on add-on cards that I've used but now removed, or on hubs) do not work - but some do).

*I wonder if it has something to do with one of the following:
the RAID card I'm using being incompatible - the board includes Nvidia's simulated RAID but I wanted to replace it with a card, the card uses the other PCIe slot (the graphics card is in the main one)
*a duff/damaged motherboard or BIOS
*a duff graphics card
*a duff PSU

I suppose the first is most likely but wanted to find out if anyone can see what the cause is, before I try changing things.

thanks,

All the things that you are describing are do to bad BIOS.
Use other PC to download BIOS look for the latest one.
1. DO NOT INSTALL BIOS THROU WINDOWS.
2.DECOMPRESS FILE TO FLOPPY.
3.INSTALL FLOPPY
4.UPDATE BIOS AT BOOT UP.
5.USE THE FLASH UPDATE PROCEDURE.
here is the page to the BIOS flash up and how to http://www.abit.com.tw/page/en/download/guide.php
hope this helps.
be careful make sure you get the right Bios.
it is easy to make a mistake and damage your board.