Run HijackThis and check the following:
O4 - HKLM\..\Run: [Explorer] C:\WINDOWS\SYSTEM\EXPLORER.EXE
O4 - HKLM\..\Run: [MyCometCursor] C:\PROGRA~1\COMET\MYCOME~1.EXE -quiet
O16 - DPF: {6B4788E2-BAE8-11D2-A1B4-00400512739B} (PWMediaSendControl Class) -
http://216.249.25.152/code/PWActiveXImgCtl.CAB
Click FIX CHECKED
Delete the following file:
C:\WINDOWS\SYSTEM\EXPLORER.EXE
Try
Clean-booting your machine until you notice what is causing the icon. Then post the information you found back here along with a new HijackThis log.