My sister's M1530 started acting up two months ago, the screen would flicker, shut off, or completely not turn on anymore. I figured out it was most likely the nVidia graphics card that had gone bad, since the computer would boot and load Windows, but the screen would never turn on.

Long story short, I replaced the motherboard, and the issues are continuing, yet they've become stranger. The screen turns on now, but whenever I do something specific in Windows or move the computer abruptly, the screen freezes, and there's nothing I can do except reboot it manually. Here are some examples:

1. Open up Firefox, and type "S" in the address bar and it freezes. At first I thought this was a fluke, but it's happened over and over again, and it only seems to work with the letter s...

2. Move the computer abruptly or remove/insert power cable, and the screen freezes.

3. It also randomly froze 3-5 times when I was copy-pasting folders from the HDD to an external drive.

There's probably nothing wrong with the OS, because I've swapped the HDDs with another computer.

What could be the problem? Is it another bad motherboard? Is there another component that might be causing such an issue?