Everything comes up just fine until I login to Vista Ultimate on my HP-Compaq C765TU Presario laptop. The Welcome screen comes up & then goes to black with just the cursor staring me in the face. I bring up the options page on the desktop by hitting control-alt-delete & run Task Manager to see that explorer.exe is missing from the processes. I open a new task & run explorer.exe, & the desktop comes up normal. So, what can fix this problem?