iMac has been acting funny?

[RainbowSnow]

I have only had this iMAc since late April of 2011 but, in the past 3 weeks I had strange occurrences with my iMac.

(I used a password to log in so I never logged into the system, it just said safe boot on the log in screen)

It started it self up in safe boot once. I called Apple and they said it may of been a button stuck on my keyboard but I know that's not possible because my keyboard was not even connected and despite my best efforts to tell them, they wouldn't listen.

A day ago the night I shut it down it took a lot longer than usual to shut down and it did the same thing, booted up in safe mode.

Today, I tured on the computer for the first time all day and the message
"You need to restart your computer" appears.


Can there be any explanations as to why this is happening? Is it system problems, malware, network connection issues (even as far as somebody hacking?), or just common errors that happen every now and then?

I don't download any unsafe programs, every program I have on my computer are safe and trusted, so no material is coming on here that is "unsafe" but...

Should I be worried about it being a threat such as malware or somebody "hacking"?

Thanks for your help!

//Edit//
Last night I did have a update (i forgot what it was that updated but it was a system update from Mac)

 

[Pistolator]

I believe the latest update was for Java.

Try booting up from your install disc/USB stick - with it inserted, hold option-key at boot to get a selection of boot drives.
When the installer opens, select Disk Utility from the Utility menu.
Run Disc Repair, then Repair Permissions.
Restart.

If problem persists, try resetting your PRAM (parameter RAM that holds basic settings). During the boot process, hold down CMD-OPTION-P-R.

Failing that (I forget what it's called), shut down the computer, pull out the power cable for 30 seconds (to wait for any residual power to dissipate), then plug back in and restart.

If it still fails, talk to Apple. If it's only a few months old, warranty will take care of it.