Problem with share folder and printer in windows 7

hello guys...
im about to give u a problem that i have for almost 3 weeks now..

recently, in my office, we upgraded from XP to win 7.everything was fine before until win 7 come to the scene....

so, we have 1 pc that act as main pc to save all document and data.and we share that folder to 4 other PCs in the office.

it work fine for like 3-4 days, then i cant access the shared folder anymore and have to reconnecting the other 4 PCs to the main pc again.

here is what i did:
- connect the 4 PCs to main PC via pc name.and mapped drive.
- use static ip on all 5 PCs.

some more info:
- main pc use windows 7.the other 4 using windows XP.

- all 5 PCs use F-secure v9 anti virus..(yup, i suspecting win 7 and Fsecure has something to do with this problem )

- all 5 PCs joined domain..but already use admin password to connect before.and work for 3-4 days without asking password everytime we want to access share folder.

any help is welcome..thanks in advance....


**edit
printer also suffer the same fate as PCs

ermm..i guess there is no solution for this one...