Various problems on Macbook Pro

Question

Hello everyone. I know this is a long write up but I would really appreciate any help. I bullet pointed the problems to make it easier to follow. I have a Macbook Pro which I bought in August of 2010. Lately I have had various problems that become very frustrating. Here are the problems:
-The first problem is that when I shut my computer and then reopen it, the wifi display on the top has no bars. When I open up network prefrences, it shows my home wifi as available but when I click it, it says "cannot connect because the connection timed out." I try turning the wifi off and then back on but this doesnt solve the problem. My only resolution is to completely restart my computer. I know it is not my router because all the other computers in the house run fine.
-Another problem is that many times I cannot open firefox. I click on it and it says "Cannot open firefox. The application is already open." but it is not open because I had not opened it the whole time and if I go to force quit, it doesnt even show up in there.
-iTunes will not open up many times also. This error message says "The iTunes application could not be opened. An unknown error occured (13014)."
-If I try to throw something in the trash, an error message pops up saying "An unexpected error occured (-50)." This message also shows up if I try to create a folder.
-Safari will open up with a random page that was viewed earlier, but not the latest page viewed. For example, if i read a couple articles on yahoo, then watch a couple videos on youtube, then go on facebook, and then quit safari, if I open up safari again, one of the yahoo articles will pop up. I disabled that setting that opens up the last viewed page but its not the last viewed page that opens up anyways so thats not problem. Also when I open safari, it wont remember any changes that occured like new bookmarks or any of the history that occured after the site that pops up. Going back to the previous example, when it opens back up on one of the yahoo articles, it wont have the history of the youtube videos or facebook pages that were opened after the yahoo articles.
-Google Chrome will open but it wont go to any websites or anything, just a blank screen.
-When firefox and chrome arent working, safari will open up any page except Apple Help pages. Its as if this problem is keeping me from trying to fix it.
-When 1 of these problems occur, all the others occur. If none of the problems are occuring, the others arent either so I believe the problems all come from one source. Possibly a virus?
I have found online some solutions such as restarting the computer and holding control+command+P+R. This did not work. I brought it into the Genius Bar at my local Apple Store and this is the first time ever I have been dissatisfied with my visit. The guy just told me a possible fix and was done with me in 5 minutes. It would have been more helpful if he actually did the fix and see if it worked. Anyways, he told me to restart and hold Command+R. I had all my music and pictures on a flash drive so I was fine with clearing out everything. So when I did this sunday night, I cleared the hard drive and reinstalled Lion. I was surprised that it actually worked like normal that night. It worked perfectly fine this morning also but when I came back to use it again around 5:00pm, the same problems occured. I will probably end up bringing this back to the Apple Store and I hope this time they take it in and try to fix it. If anybody has any resolution at all, please help. Thank you.

Answer 1

With the Finder active, press the following key combinations, in this order:
Shift-Command-H
Command-3
Command-I
The Info window for your home folder will open. Click the lock icon to authenticate. In the Sharing & Permissions section, you should have read & write access. If not, make it so. Select "Apply to enclosed items" from the action (gear icon) menu.