Power-up Issues

[StormRoyale]

Howdy y'all.

Disclaimer: I am long winded and not tech savvy.

My system is about 2 years old and is typically left on most of the time.
Starting about a month or so ago, whenever I would turn it off, I was occasionally having issues during powerup. The system will power on, but not "boot".
Today was the first day that I couldn't get it to boot no matter how many times I turned the power off and on. Sometimes the hard drive light on the front of the case would light up, but most of the time it wouldn't.
After opening the case and fiddling around a bit, I was able to get the system to startup the bios if I unplugged the main hard drive. So I believe the problem may lie there.

How can I tell if the problem is with the hard drive, it's cable or even the motherboard?
When the system is powered on and everything is running as it should, I have no problems. No lock-ups, nothing... even if I leave my system on for days. That would make me think that it wouldn't be the hard drive itself... but who knows?

Thank you for any help y'all can provide.

~Vanessa

 

[Dangman]

It would help if you could list all of the specs for your PC, including the exact make and model of the PSU.