Sign in problems on my mac!

Question

Hi there!
Really hope someone can help me.
My mac won't allow me to sign in. When I enter my password and submit it just "thinks" for a time, a quick blue screen appears, then it turns white and just return to the sign in screen and nothing happens.
The same issue with the guest user. What can be the cause of this?
When I start the Mac in safe mode it allows me to sign in, so is there something I can fix?
I really hope I don't need to recover my MacBook Pro, because my back-up from TimeCapsule is pretty old and I can't make a new one in Safe Mode :S

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
Third-party system modifications are a common cause of usability problems. By a “system modification,” I mean software that affects the operation of other software — potentially for the worse. The following procedure will help identify which such modifications you've installed. Don’t be alarmed by the complexity of these instructions — they’re easy to carry out and won’t change anything on your Mac.
These steps are to be taken while booted in safe mode.
Below are instructions to enter some UNIX shell commands. The commands are harmless, but they must be entered exactly as given in order to work. If you have doubts about the safety of the procedure suggested here, search this site for other discussions in which it’s been followed without any report of ill effects.
The commands may line-wrap or scroll in your browser, but each one is really just a single line, all of which must be selected. You can accomplish this easily by triple-clicking anywhere in the line. The whole line will highlight, and you can then either copy or drag it. The headings “Step 1” and so on are not part of the commands.
Launch the Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
When you launch Terminal, a text window will open with a line already in it, ending either in a dollar sign (“$”) or a percent sign (“%”). If you get the percent sign, enter “sh” and press return. You should then get a new line ending in a dollar sign.
Step 1
Triple-click the line of text below to select it. Copy the selected text to the Clipboard (command-C). Then click anywhere in the Terminal window and paste (command-V).
find /Sy*/L*/Ex* -type f -name Info.plist -exec sh -c '/usr/libexec/PlistBuddy -c "Print :CFBundleIdentifier" "$1" 2> /dev/null | egrep -qv "apple|Accusys|ArcMSR|ATTO|CalDigit|HighPoint|hp-fax|JMicron|print|SoftRAID|stex" && echo ${1%*.kext/*}.kext' {} {} \;
Post the lines of output (if any) that appear below what you just entered (the text, please, not a screenshot.) You can omit the final line ending in “$”.
Step 2
Repeat with this line:
ls -1A /e*/mach* {,/}L*/{Ad,Compon,Ex,Fram,In,Keyb,La,Mail/Bu,P*P,Priv,Qu,Scripti,Servi,Spo,Sta}* L*/Fonts 2> /dev/null
Important: If you formerly synchronized with a MobileMe account, your me.com email address may appear in the output of the above command. If so, anonymize it before posting.
Step 3
osascript -e 'tell application "System Events" to get name of every login item' 2> /dev/null
Remember, these steps are all copy-and-paste — no typing. Also remember to post the output.
You can then quit Terminal.