I have an HP Pavillion desktop a600n with XP home service pack 1. I'm positive there are viruses and/or malware on my computer and I tried to install TrendMicro Titanium 2012 edition but it said I need the latest service pack. So, I downloaded Service Pack 3 and when I tried to install, I received the following error: the file C:\windows\system32\drivers\ndis.sys is open or in use by another application. close all other applications and then click Retry.\ I read the thread about the the 4 step preliminary instructions but I did not attempt to follow them because I was uncertain if they would even install on my computer since it doesn't have service pack 3. Any sort of help would be greatly appreciated. Thanks. I apologize if this is in the wrong section.