Windows XP problems - What is going on?

I have a couple of issues that just cropped up. I am running XP Home SP3. I have ran every virus, bug and spyware program that I have. I have AVG Free, used Ad-Aware free, Windows Defender, SuperAnti Spyware Pro and a couple of on line programs such as HouseCall, ect.

My current issues - When I left click to get a drop down menu, it is many time empty. No menu - the the IE will open a totally new window. I close the open window, go back left click to get the drop down and blank - then the new window will open up again. This does not happen all of the time. I can run Foxfire with no problem. The drop down it there.

My second issue - I can no longer click Start - Log off - Switch User. I can no longer switch quickly between users. When I click it nothing happens. Yes, I went to Control Panel, User Accounts and clicked on Change the Way Users Log On and Off. The second box is not checked "Allow Fast User Switching". I can check the box and then click Apply Options - but when I come back - the box is still unchecked. I tried to unchecked the first box, but that just grays out the second box. What is going on?

Third issue - when this all started to happen I noticed on more change in my system. Many times I will hit the sleep button on my computer if I step away. When I come back, and press the sleep button again - the main screen with known user accounts will come up and I would enter my password. Now - when I come back all I get is a little box in the middle of the page for me to enter my password. I can't remember what is says - but the user name not the same as on the log on screen with the listing of user accounts. It says something like Owner or Administrator? Something. I would check to see what it says but I am afraid I would loose everything I have typed thus far.

Any idea what is going on with this? I thought it might be a virus - but everything I run says I am clean? Any suggestions??