Nice guys, but my computer has never worked well s...

Nice guys, but my computer has never worked well since coming to these guys. They replaced a hard drive and then reverted my computer back to an old operating system. Terrible. They didn't replace the drivers correctly, so I had to go back. (they, of course, tried to place blame on "something I'd done" to cause the problem before they figured it out and got the machine going again.) Two months later, the hard drive they replaced is now failing periodically. "No boot device found." Seriously???!!! Not sure yet if I'll go back or seek help elsewhere...