Can't see computers on network

Good day all,

PC1 (Windows XP), PC2 (Windows XP),
PC3 (Windows 7), PC4 (Windows 7)
- Connected all to a wireless router;
- Same Workgroup
- All C drives are shared and with full permissions;

When I click on Network, I can't see any of those PCs!!

Please advise.

Thank you

Dear all,

Just solved the problem;
I had to make the network 'trusted' in my internet security application (Kaspersky).