Explorer.exe Error On Startup

Windows XP Media Center Edition w/ SP3.Every few times I turn on my computer, there will be an error regarding explorer.exe (something like the something failed to initialize at *some random letters and numbers*). When I then log onto any user accounts, including administrator, the screen will not load. I will sit staring at the wallpaper with no taskbar or desktop shortcuts. The only thing I can do is the *windows + L* to switch user and log out, or CTRL+ALT+DEL to get to the task manager. There will be an abnormally low number of processes running (in the 30's). I will have to restart the computer and hope for the best on my next try for the computer to load.

Also, a similar problem. Occasionally (1 out of every 4 tries or so), when one user is logged in and hits *switch user* (but stays logged in), no other users may load. When the other users try to login, they are instantly logged out to the blue login screen again. You can see the background for possible a half of a second before getting logged out. There is no error message or anything of the sort.These errors all have come up in the past few weeks. I am stumped and have no clue what to do.