My eth0 is gone

[* Tong* <sun_tong_001@yahoo.com>]

Hi, 

Hysterically, after I reboot Debian, my eth0 device is gone. 

% networking start
eth0: ERROR while getting interface flags: No such device

% ifconfig eth0 inet 192.168.0.99 up
SIOCSIFADDR: No such device
eth0: ERROR while getting interface flags: No such device
eth0: ERROR while getting interface flags: No such device

Luckily, I managed to get it back. I'm just wondering, 

what could be the reason that I lost my eth0? I remove the
discover package, could it be the reason? Is discover package
really necessary? 

I get it back by 

modprobe sis900
depmod -a

Can the effect last beyond next boot (and beyond)?  

Thanks