I had a similar problem, but it was on a Win98 system. When it tells you that you have:
"ERROR: Himem.sys has detected unreliable XMS memory at address 00FD7800 XMS Driver not installed"
The XMS is the "Extended" part of memory.(EMS is "Expanded" part of memory)
This is what you might want to do, it worked for me. Take out any of the memory that you just had installed. Leave the original in there and start it up. If it starts, then the original is good. Just keep addin' one at a time and starting it up, till you get the error to come up again. If you get the error with the original when you first start, try moving it to a different slot and see if it works. Otherwise, just keep addin' the memory back in till you get that error to come up again.
What I'm guessin' is one of your memory sticks has gone bad, or one of the slots for your memory is acting up. With memory, you should make sure you buy the same kind for all your slots and make sure the connectors are the same, if you got gold-plated connectors on the board, make sure your memory is gold-plated also.
What you stated up above was exactly what was happening to a system I worked on. Hopefully this works for you.