ASUS MB Realtek device not recognized

Upgraded XP PROsp2 w/ASUS P5WD2-E Premium Motherboard+Pentium D+DDR2 mem. MicroS says “Not Digitaly Signed” on ASUS CD Realtek install…system STOPs x 7E err or just reboots. No Sound dev found in CP. Other audio specs check OK. ASUS support says only solution is COMPLETE REINSTALL OF XP (to bare disk)!
Unacceptable…I have 8years+ of Apps. BkUp and restore would only bring problem back. I LIKE my music!!!