It's likely one of two things: weak power supply or a PCI IRQ channel sharing problem.
I would highly suspect the IRQ channel sharing problem since you have an SBLive and that card is VERY prone to this problem (this is NOT the same as an IRQ conflict). More details on this problem here:
http://soldcentralfl.com/quakecoop/glfaq5.htm#5_9
Since it sounds like it's an easily reproduced problem (you implied it happens every time you run a game) it'll be easy to test.
While I suspect the SBLive is the culprit, keep in mind there are other PCI cards that can also cause this (less likely nowadays, but it happens). I've seen it with PCI Modems, PCI NICS and PCI SCSI or ATA controllers.
I recommend pulling the SBLive card out of the computer and try running a game and see if it freezes or reboot (most games will run fine without a sound card).
If pulling the SBLive doesn't stop it from happening, try pulling ALL your PCI cards (make a note of which slot each card was in before pulling them!) and see if it still happens. If it continues to happen then I'd suspect it's the power supply.
If pulling the SBLive doesn't fix it but pulling all your PCI cards does, then you should install each card ONE BY ONE (and put them back in the same slots they were in) and test it until you find the culprit. When you find it, try moving the card to a different open slot.
If it's the SBLive that's causing it (as I suspect) then try moving it to another empty slot first.
If it doesn't work properly in any of the empty slots then you'll have to pull one of the other cards and try it there. If it works then put the card you swapped in one of the free slots. When you do this try VERY hard to arrange your cards so that they don't share BIOS IRQs (after the POST screen, BIOS displays a screen that shows everything detected by BIOS - memory, hard drives, PCI cards, etc. It will list the IRQ for each card) try to arrange it so that AT LEAST the SBLive and the Video card are not sharing an IRQ with anything else (if you have a lot of cards it's hard to avoid sharing IRQs).
Frankly, if I were you, I'd ditch the SBLive and use the on-board C-Media sound. It sounds just as good to me and won't give you the IRQ hassles. That's what I did when I upgraded to an IWill XP333 - I was elated to be rid of my flaky SBLive.
Hope this helps...
