Computers fans only turn on when ONLY the power is plugged in.
About a year ago, I came home and tried turning on my pc and all that happened was the green power light turned on and straight off and the fan barely spun. I moved not long after this and decided to try again, just turning on the tower itself. Now the fans and green light both turn on, but the BIOS did not enter. What I found was when I added something extra to the PC, say my speakers (which are powered between the power cable and the computer itself) or my mouse and keyboard, and turned it on, it wouldn't turn on with the fan spinning barely again. In the Summer, I did work experience with my schools IT department and from what I said they got me to change the BIOS battery as for about half a year before it stopped working, the time on my computer would reset after being off for a certain amount of time, an amount that got smaller and smaller. Changing this BIOS battery did not help. Now, my friend who knows more about PCs than me reckons a power surge could have killed the motherboard but as his side is more coding, he wasn't too sure. But I have been doing some research online and apparently it could be the PSU. So what do you think because I'd really like to get it working again and don't have much money to fix it myself (as I am 16) but I do have some old motherboards and I think a PSU (perks of work experience) and if not, my friends who did it as well should have. Any ideas?