No longer able to connect to each others hard drives..

so, for the first couple days, my brother and i could connect to each others computers no problem and mount each others hard drives. Boy did that make life simple.

Now, for NO REASON taht we can see..havent ran updates, havent changed a thing...when we login to each others machines, we get the incorrect username/pass

Basically i would go into his room, find my dual G5 from his iMac, when asked to connect w. username/pass, id enter MY name and password, and it worked flawlessly.

So what the heck happened? Ive enabled remote login. Ive checked the firewall/Accounts settings. Am i missing something?

thanks in advance!