Admin account disappeared after reboot

I really hope someone can help with this. I'm using os x lion & mostly haven't had any issues. Its been updated when updates are released. This morning I shut down my Mac & a few hours later when I turned it on it took about 4 minutes or so before going to the login screen. The only account showing was guest. My admin account wasn't there. I'm the only user so have always used admin. I logged in under guest to do a search on the Internet for the problem & noticed everything was taking forever. I have super high speed Internet so this was kinda weird. I did the command r, terminal, in order to reset my password to create a new admin account but when I select Macintosh HD to give me the option to select root I get nothing but the spinning wheel. I waited forever then finally shut down my Mac. Tried again & same thing. Then I thought maybe reinstalling lion may help (I read that one of the updates was to fix the admin account disappearing). I thought maybe somehow This fix may have screwed some of us that didn't have the problem to begin with & maybe a reinstall would fix it up. Nope. Lion wouldn't reinstall. Now I'm not only missing my admin account but stuck trying to reinstall lion which keeps telling me it can't download all of the components to do the reinstall.

I've also run the varify & repair for both the disk & for permissions but didn't work. I have the disks that came with my Mac & also have the snow leopard disks & tried to erase the hard drive to start from scratch but it says it's unable to erase. If there's a way to reset my Mac to a fresh out of the box state I'd be willing to do that since I think I'd only lose some pics & nothing really all that important.

Boot from the Snow Leopard disc and go into Utilities and run repair Disk. What you are describing typifies a failing hard drive.

Thanks harry. I do wonder if the hard drive is pooched but seemed to happen out of the blue. I've heard that a hard drives typical lifespan is around 4 years & that's how old my Mac is.
I talked to someone at the Mac store & they think from what ive told them that there may have been a software issue before I originally installed lion. I did have some issues after initial lion install back when it was released & had to create a new admin account but everything was smooth till I shut it down Sunday after the update. I'm heading back to the Mac store now so they can have a look at it.

Yup. Hard drive failure.