...safe mode and see whether your account appears, or whether you can sign in as Administrator. If able to, then use System Restore to roll back. Alternatively, choose "last good configuration" at the boot menu (instead of Safe Mode).
I set up a guest account for a housesitter to use while I was away. Since I've been back, I can't get into my accoutn. It's not on the options when signing in, and the only place I find my account is when I right click Start and explore. When I click on my accounth there, it says access denied. I also can't sign in as administator. I've read some advice to similar problems here, but nothing seems to work. What do I do?