We assume both PC's are in same VLAN.
1.See the statistics of interfaces connected to 2 PC using "show interface" command
2.See the error counts like CRC etc., whtether the are increasing.Also see the reliability of the connection.
3.See the speed & duplex settings of the connection of PC to switch, try to keep it as auto.
4.Try connecting othe PC on same connection and then see whether packet drop is there.
HTH...rate if helpful..