I agree with Speedo that your "hissing" power supply could have damaged your mobo, at least maybe blow a fuse on the mobo. Not being sarcastic here, but the sequence he's probably thinking is...The processor fan wasn't spinning and the Power Supply was making a really high pitched hissing sound. I went and got a new one, and put it in. Afterwards, it was exactly the same as it was BEFORE the Power Supply blew, so, I don't think it was that the Power Supply damaged the mobo...
1. Attach bad supply to good mobo, turn on.
2. ZZZZZAAAPP!! Bad supply damages mobo.
3. Repeat the zapping 20 times while trying to debug.
3. Replace bad supply with good supply, turn on.
4. The earlier damage prevents mobo from working.
Just yesterday I learned my own mobo has at least some fuses, but I don't know how many or which circuits are typically protected. Their primary purpose is to protect the $500+ mobo/CPU from the damage a bad $50 switching power supply can cause. Not being user-replaceable, they're not something the mfg. typically points out on the diagrams, so you'd need to poke around to find them to test them, if they're there.
Sounds like your supply is OK now, at least the non-ATX- connector part of it, since fans turn and the other devices light up. No beeps is common, a lot of mobos don't beep anymore, at least not audibly. I'm thinking your monitor is probably OK too, because they are pretty indestructible unless you drop them....and ever since I haven't been able to boot, at all. No display, no boot beep. The fans spin, the CDRW ejects, but it doesn't boot.
You mentioned maybe forgetting to hook something up. I doubt this next idea is it, since you earlier got a Biostar logo onscreen, but some mobo's do watch for your fans to be turning: if they dont see rotation signals coming from the fan, they won't turn on. So you have to actually connect fans to the fan connectors on the mobo, otherwise you won't have the signals. I'm not talking about fans that have the same kind of connector as you plug into --or between-- a HDD or CD; those won't supply any rotation signals to your mobo. No, the fans must be 3-wire fans, with a rotation signal wire on the end opposite the end with the black ground wire, power on the center wire, of a little 3-pin connector. Or maybe you could have a bad fan that's not putting out its rotation signal. As I said, this idea is pretty far-fetched.
Well I think if your brother's AGP card was partway un-inserted when the power was applied, your brother's own PC could have damaged his video card, or perhaps the Northbridge-equivalent chip on his mobo if his AGP runs through that chip. He might just have been lucky it didn't blow the other times the card popped out, it depends on which pins are uninserted. Always screw down the add-on boards.my brother's computer doesn't have screws on AGP/PCI slots... he lost them a long time ago and never bothered buying new ones. I kinda jiggled the graphics card out of the AGP slot after plugging it in, because this happens ALL the time, just doesn't give any display after jigging it out then back in, resetting has always fixed the problem, until now. I reset the computer, and it hasn't booted since.
Just so you don't feel too bad, this screw thing in your brother's PC, was avoidable. That his PC broke while you were debugging yours, is just a coincidence, one that could have even happened any time he reconnected his monitor himself.
Try giving your video card to your brother as a peace offering and maybe it will get him going again, or at least will help narrow his problem down. Or if his Northbridge AGP is blown, a PCI-based video card might still work in his PC. Compared to the cost of a few screws, even both solutions are painful, even if they work.
The bad power supply in your PC was not avoidable, not something you could have predicted before turning it on. Other than checking fuses for continuity, I'd either send the mobo back for repair or take the whole rig into a shop.