Hi all. I am new to EE, and this is my first post/question. I am the IT Director for a doctors office with about 100 end users. In the last 5 days, I have had 5 PC's suddenly lose internet/network connectivity. All are W7 Pro, 32 bit machines. Symptoms are complete corruption of the TCP/IP stack and loss of DNS functionality. I have run full system scans on all using MalwareBytes, and Kaspersky rescue disks. Neither have found any evidence of virus or malware infections. I have exhausted all of my resources trying to fix this issue, and have resorted to re-formatting 2 of the 5. (I was able to resolve the problem by doing a system restore with the other 3). If anybody else has seen this, please advise. I can provide more details on steps taken to resolve as replies come in. Thanks in advance for any help you might provide.