Can i run mining on one wallet at more than 2PCs?
Please clarify your question? Do you mean you are pointing 2PC's at the same address? Like -miningaddress="address" bc this is just fine to do.. Do you mean that you want to pool both PC's resources to the same wallet?
i mean that i will copy this wallet.dat to PC2 and run PC1, PC2 at the same time

I'm doing it this way and it works fine.
for me to
Hashes are combined?
I'm also using same wallet on 2pcs and, so far, no problems.
I believe the hashes are not combined, its just like 2 solo cpu mining with mining rewards being sent to the same wallet.
CH