There are many third party apps which may combine with MacKeeper to cause problems for your computer. See the following for guidance as to how to rid your computer of this beast.
But you still have to gain entry to start the process and the symtoms you mention are in keeping with HD problems.
If you have another mac available, use FireWire Target disk mode.
Connect both macs with a Firewire cable, Your mac acts as host, your friends mac as target.
The harddisk of the target will show up on the host like an external harddisk.
So you can start backing up from there.
here's how to:
If there are many things on your mac you can't afford to lose, then you can't afford not to make regular back-ups!
At least one bootable clone, preferably two. One to keep at home, one somewhere else (to protect from dataloss in case of fire, burglary,...)
And if you have that, you can add Time Machine as an extra, which has some other advantages/disadvantages. (more regular, no work, but not bootable and less reliable), and can return your machine to the state it was in, x days/weeks ago, when you didn't have the problem.
Take the machine to a local PC/Mac software repair place, tell them what happened and you need data recovery performed and the system restored.
You can opt to wade through all this I wrote, but it's going to take time and you can't afford to make a mistake, your rather early in the self repair of Mac's stage still.