Complicated problem: Laggy Macbook Pro, now not booting

Question

I am facing a very complicated issue with my unibody Early 2011 15" Macbook Pro (2.2 ghz core i7, 4gb 1333mhz ram, amd radeon 6750m, if you need hardware details).
I guess the issue started after my computer started to get laggy for no reason at all: it was never the GUI that lagged, but whenever I would perform some data-dependent tasks such as playing a video, or trying to open a big file. This lagging did coincide with some of my friends playing around with magnets around my computer (which may have possibly corrupted hard disk data).
After it got laggy, another major problem hit my MacBook, where I plugged in an old, broken USB into one of the ports by accident, and the computer suddenly shut it self off. The computer then seemed to have no power at all, with no response to pressing power button, or the battery indicator button. I feared the worst: that my logic board had been fried, so I immediately took my computer to the Apple Reseller. The technicians there said it was no problem at all, just that my motherboard had shut itself of in order to protect itself from a USB power shortage, and he unplugged and replugged this one small component on the logic board, which I am guessing is the Power Management Unit, and my computer miraculeously started booting.
So then, I get back home, and the laggy problem is still there. I just had to cope with the problem for a few days, until I go back to the Apple Reseller, but then suddenly, after a restart, the computer started not even booting. The grey apple icon would blink, and turn into a circle with a cross icon. Checked online, and this is apparently related to corrupted system files. This is where I began to suspect that the USB shut-off from few days ago, did more damage than the technicians thought: maybe related to the hard disk, or RAM.
But then again, it could have just been a coincidental corrupt hard disk from my actions, so I wiped/repartitioned my hard disk, and restored the OS and my files from a TIme Machine Backup. Again, the problem was still there, so I thought it might be to do with my backed up system files, so I did a fresh install of Lion.
The fresh install of Lion seemed to eliminate all lagging problems, but after I started copying my files and installing applications from Time Machine, the lagging problem gradually returned. So another question arose, was it a faulty hard disk, or a corrupt file or application that was making it laggy? To check if it was my hard disk, I did a zero-over erase of the entire disk with Disk Utility, and sure enough, the writing process failed in the middle.
After thinking I zeroed in on the problem, I replaced the hard disk in my Macbook Pro with another 750gb Toshiba SATA drive, and did a clean install of Lion. Once again, the laggy problem was gone, but just like the old hard disk, the laggy problem returned after I started copying files over and installing applications. Switching applications would take forever, and accessing folders on my hard disk would also be laggy. Playing videos was impossible, but the GUI (dock, spaces, etc) were all very responsive.
Now, I thought the problem is either with faulty RAM, or my hard disk reader is broken (since two hard disks, although the original one was faulty, both failed). I read online that the Apple Hardware Test (AHT) can help identify and pinpoint hardware problems, so I inserted the 2nd disk that came with my computer (Applications Install), and pressed D, but then nothing came up. After countless attempts, I maybe thought it was the wrong disk, so I inserted the 1st disk (OS Installer), and held D while booting, but still, AHT would not load.
After countless attempts at loading AHT, all of which led to me forcing shut down/holding power button after seeing the Apple logo, brings the problem to where I am at now: my Macbook does not boot into the login screen. After the Apple logo, and the spinner wheel have appeared, the screen turns white and the display becomes an infinite loop of switching from a gray color, to a white color.
This problem is frustrating me very much, because there are so many possible causes, and the problem persists even after reinstalling the OS, and even replacing the ard drive. The logic board shutoff could be the cause, but then again, the lagging problem started way before it happened. Somebody please tell me what is the problem, and what I should do? Thanks in advance.

Answer 1

novaria wrote:
Didn't know my magnets were strong enough to corrupt hard disks.
Yes, it's a method used to destroy data on a hard drive as it's recorded using magnetic fields, either "on" or "off" to represent the 1's and 0's that make up the basic building blocks of your data.
But, the magnet does not explain why the hard disk reported an error when being erased with zero-over option.
When the driver software has a problem reading the data on the drive, it assumes it's a bad sector, then maps it off and uses a spare. You likely ran out of spares.
I just tried zero-over erasing the second, good hard disk that replaced the original, but again, it fails. Is this a common problem with the zero erase option?
No.
or is it something to do with my hard disks, or some sort of damaged hardware in my computer?
Well this is drive #2 and it's new, and you get the same problem.
It's either something your doing, (like moving the hard drive/ computer while it's operating thus the heads are striking the platters) or it's a hardware defect, or perhaps the magnets did other damage we can't see, perhaps it's magnatized the computer and that's affecting the hard drive or electronics.
May be a loose or defective cable.
It's time for a hardware evaluation at this point.