In task manager did you just check "Applications" only or did you also try clicking on the "Processes" and " Services" tabs?
The reason I ask is there may be more running in the background than what is shown in the "Applications" tab. In the "Processes" tab watch the CPU usage numbers to see what else may be running and if so what and where. Operating system, browser, Adobe, antivirus updates as well as full system virus and malware scans running in the background can last a long time sometimes.
