I am having a problem with my laptop for past 3-4 hours. Initially I got the alert from Sophos that infected items have been moved to quarinteen. And I tried to clean them up using sophos. "yoa.exe" was not getting cleaned up and I manually deleted it. Now no alerts are coming. However, when I try to access any application via clicking on the icons I see the "Open With" Box. I tried to link 1-2 of those(for e.g. iexplorer) nut again and again the Open-With box appears. I went through your suggested initial steps and have generated OTL logs (attached with this post as well). Your help in resolving this issue is highly appreciated.