black screen on startup with "my computer" open

hi. i know that this problem is quite common but i still cant find a working solution.

i hav been using windows 7 home premium for quite a while already but today suddenly the black screen problem occur. my explorer.exe is already running. i cannot access the internet coz my internet browsers (and few other applications) have been blocked by my antivirus (microsoft security essential). the antivirus suspected the applications as trojan so i uninstalled the antivirus. but after that the applications are still blocked.

i hope u guys can understand what im saying. thx in advance

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