ICS not working after 5pm

[IF]

I have this strange problem with internet sharing with 1
client computer running Win XP, the other running Win ME
OK, Host computer running Win 2000. After 5pm, the client
computer running Win XP loses it's IP address and can not
get another one, thus can not connect to the shared
internet. What is strange, it works from about 9am-5pm
every day great!
Any clues what is wrong here or a setting I can check?
Thankyou