I can`t boot the system after upgrade!

It`s me again, sorry! this time Itried to be more specific about my problem!

I upgrated the computer with the mobo Asus a7n8x E deluxe, 512 Mb RAM pc 3200 and the AMD athlon xp 3000+
After I put everything together, I started the computer and the first thing that appear is the asus utility,
so I upgrated the bios with the rev. 1012 (everything is been fine).

My problem is:
when I start the computer, first there is still the asus utility
( you know........press. alt+F2 to enter Awd flesh utility)
and then there is a the regular black screen wich says:

Phoenix AwardBios v6.00PG
ASUS A7N8X-E Deluxe ACPI Bios rev.1012
AMd Athlon xp 3000+
Memory testing 512Mb OK
Primary master Maxtor 546673838
Primary slave Maxtor 323442345
Secondary master Memorex 52Max 4545444
Secondary slave none

Warning!! Case Open Warning

If I press DEL I can enter the setup

(at this point I can`t do anything except go into the bios!!)

the computer seems to see everything: Ram, 2HD, CPU, CD room, the floppy (because I could install the new bios), the new FAN that I bought works fine, so I`m traying to say that every single component (except the mobo mybe!) works fine.

In conclusion I was traying to reinstall windows but I couldn`t because I can`t boot the system both Cd room and floppy, (and of course I changed the order in the bios!)

when I put the boot disk in the floppy drive and restart the computer the first thing is one beep from the mobo and then the floppy start to load because I can hear some noise, but then nothing!

I tried also to reset the CMOS but nothin happened!

I don`t know what to do anymore can you help me please!
Sorry for my english, I`m learning!