Symantec was recently installed, replacing Avast and I have seen nothing but problems.?

Is it just me, or are there definite problems with Symantec and Vista? I am running Windows Vista Business edition. This is a desktop computer at work. We are connected to a Windows 2005 or 2008 server. My problem: for about the past 2 weeks, I have been receiving 'critical' errors in the error logs about Kernel-Power, event ID 41. Says sleep transition not successful. However, what I am seeing as the end user is: Outlook is the first to lose connection with the network. Then, because Outlook is trying to connect to the server, it begins to interrupt other programs. Typically, the internet is the next to lock up, then other programs follow. The only thing to do is hard boot the computer. I start in Safe Mode, then restart into Normal Mode. This has happened consistently each day of the working week for two weeks now. My computer is from July 2008 and from then to June 2011, the computer has logged only 9 critical events - all within the last two weeks. Any suggestions or insights would be extremely helpful. The company's IT person has replaced my network cable and battery in the computer. Her next step is replacing the NIC card, but I am not sure that will make a difference.