it really sounds like you could have multiple different problems..
1: hibernate option greyed out. on some boards, you need to manually enable this option in the power settings. it is very possible that a recent OS update caused this.
2: won't boot without a system disc. this could be a bad hard drive, but could also be some incorrect bios settings:
for instance-- at work, when we load pc's, we disable all bootable drives except for the hard drive-- if you did a similar thing, but left the cd drive as the only bootable drive, this would also cause this.
if the hard drive is bad, the easiest way is to test it with the specific hdd manufacturers test program(use the seagate program on a seagate drive, etc) on a working pc, or you can also use something like UBCD(ultimate boot cd) you would boot from the cd, and run a full test on the hard drive..
3. won't power up:
there are tons of things that can cause this.
listed in order of my normal testing proceedure:
3a. bad power supply. i recommend buying a power supply tester for this. you simply plug it in, and if the psu is good, the psu tester will light up and tell you.
i don't like using a different but similarly-speced pc for this, as i have had some bad psu's destroy that second test board(though rare)-- so with taht in mind, the $5 for a psu tester is well worth it.
3b. try a known working AC-DC, atx-compliant power supply.
3c. bad memory. this is the second easiest thing to check, as it doesn't require unscrewing any major components, and everything snaps together..
you will need to get a different, known-good stick of memory to test this, so it might be easier to take the whole pc to a pc repair shop, and try to find a nice tech that is willing to try to help without the need of you buying a bunch of memory.
3d. try the known-working ac-dc atx-compliant power supply with the new memory-- if this still doesn't work, then step 3e....
3e. bad motherboard. if all else fails this is the last thing it can be-- fortunately, most atom boards are cheap, and because the processor is integrated, you cannot separately test it-- otherwise, that would be the second-to-last step..