logging in makes another PC to go down

I've got a curious problem. Perhaps it's a simple and known thing but to me it's new.
I've got to PCs running W7 build 7000 ultimate x64 and connected through a router.
After I log into PC_A due to a restart or shut-down (never tried switching user) it makes PC_B to restart apparently from power failure!!! It doesn't happen anything to PC_A if I log into PC_B. Both computers have the same two user accounts.
Has it anything to do with wake on lan (or usb or keyboard)? the board on the crashing PC is a Asus P5QL Pro.
thnaks

I have updates on this issue.
The problem lies on the Realtek LAN driver.
Long story short: I have two PCs connected through a router. Mine suffers a BSOD (memory dump ndisw.dll) very rarely and I presume caused by the other one. It has a JMicron itegrated LAN. The other PC is always crashing (memory dump, not stating the dll). It has a Realtek LAN chipset. I tried a Trendnet PCI LAn card (also RTL chip) and the result is the same. I log in and the other suffers. Sometimes I have access to one another and sometimes I don't. On my wife's PC sometimes I have limited connectivity...
The drivers are up to date...