stange network problem

Hello all,

I would like to describe a very strange matter I experienced recently.
First my configuration:
- OS: Windows XP SP1; 2 instances on C: and I:
- Asus Mobo
- P4 2.8
- 1 Gb memory
- onboard Broadcom lan adapter; plugged to Internet modem
- 3com lan card; plugged to laptop
- the onboard and the 3com adapters are in bridge (XP)

Always functioned good.

Until I started XP one day (recently)
The Onboard lan port reported "cable unplugged".
Whatever I tried, I could not get it back to work.
I tried all the obvious; driver renewal, removed driver, also from
BIOS etc
Also tried other cables etc. No success.
Also the other XP instance doesn't work; even restore didn't repair
it.

BUT: when I started the computer with the BartPE CDROM; that's a
booting CDROM that makes XP running from it; no HD required.
Look at (http://www.nu2.nu/pebuilder/).
When I choose to start network support; message "installing network
components"; apllying settings and THERE it worked. I already could
tell because of the light that went on on the port of the adapter. I
could internet and all with it.
What could be wrong?

Anyone can help me with that??

Thanks!