Laptop won't boot, steady underscore upon turning on

[Manimecker]

Hello, good day.

My problem is that my Lenovo G405 won't boot up at all. It was working well until a few hours ago, I was actually watching a movie, then it started to freeze. I also noticed it was a bit slow, so I opened up Task Manager (I have Windows 7) and even when I didn't have any process using high CPU, Task Manager showed the CPU was having a 50% to 60% use, which is weird because I didn't have any program running.

I then decided to reboot it, and it turned off fine, but when it tried to reboot, I didn't have nothing, just a black screen with a steady non blinking underscore or dash. As I said, it doesn't blink, and it comes up immediately upon turning on the laptop, no Lenovo logo or BIOS, nothing. The camera LED turns on then turns off, as normal. The CPU fan comes up and stays on even with the black screen. It seems the keyboard works, because F9 turns off/on the laptop screen, even with this black screen.

I already tried:
* Taking out the RAM, without RAM the laptop makes long and loud beeps, and won't turn on, not even screen. I tried both slots, ONLY ONE SEEMS TO WORK.
* Already tried to take out the HARD DRIVE, same results. No Wi-Fi module, no optical, same results.
* I already tried 3 more RAM modules, same results.

What else I can do?

I add a photo of the problem.
http/imgur.com/31Bk82i

 

[velo3100]

Have you ran a memtest?

 

[Manimecker]

As fan as I can see, the RAM is Ok, I tested it on another laptop (because this one won't get past of the black screen with the fixed dash). I already tried 3 more RAM modules, same results.

 

[velo3100]

I would say that you should try to install windows using a usb. This should get rid of the corrupted version.