Sometimes when troubleshooting problems with a user account, the easiest solution is to create a new account and migrate your data over to it, instead of finding the roots of the problem (of which there might be many) and fixing them. The problem with migrating to a new account is OS X by default is set up to prevent access to documents in other accounts, so when you go to your previous home folder, you are blocked from viewing the files.
Additionally, while you can change the permissions for files and copy them to your new account, there may be residual permissions and settings that can either make your account less secure or result in access problems in the future. Therefore, the way to get your data to a new account folder is to first make it readable, then copy it over, and the reset home folder permissions using the utilities on the OS X installation DVD.
To start, if you have created a new account and wish to migrate your old account to it, be sure you first have a fully restorable backup of your system and also ensure you have enough time to test the new account after the migration is complete. The procedure for the migration involves adjusting account permissions, and any time you adjust permissions on many files at once there is a greater chance that an error could cause access problems.
Once you are ready, first create a new administrator account on the system. Then log into the new account and follow these steps:
Go to the /Macintosh HD/Users/ folder and right-click the folder of your old account, and select "Get Info"
At the bottom of the new window click the lock and authorize, then click the plus and add your new account name to the list of accounts.
Give your account both "Read and Write" access, and then choose "Apply to enclosed items" in the little gear menu.
When the fourth step is done, copy the contents of Documents, Music, Movies, Desktop, etc. to the respective folders in your new account (Do not do this for the Library just yet).
While you can just directly move the files from the old account to the new one, doing this will preserve the ownership and some other permissions attributes for each file, whereas creating a new copy will have these attributes changed for the new account.
Migrating the Library folder is optional, but it does contain a number of settings and application resources such as Mail accounts, and address book databases which that may be useful but may also contain corruption that could be causing the initial problems. If you want to start fresh with default settings then do not copy the Library over; however, if you want to try to preserve your old settings then do copy it over, replacing any duplicate items found.
Insert your OS X installation DVD (the gray restore DVD that came with your computer should work) and boot from it by restarting while holding the "C" key down.
Select your language and choose "Reset Password" from the "Utilities" menu.
In this utility, you can reset the permissions on your home directory, so follow the instructions to do that on your new account.
When the permissions have been reset, reboot the system with the "Shift" key held down (it boots to "Safe Mode") and try logging in to your new account.
If everything is successful, then reboot normally.
Go to the "Accounts" system preferences and remove your old account, choosing the option to delete the home folder for that account.