ah yes i just saw your other post here (so many different posts i lose track if i dont link them)
i think please let the current rebuild finish, and then you can try the cold boot, but before you power up the drobo again, can you try unplugging the power cable, and then to eject each drive (just halfway is ok) and then to gently but firmly enough push it back in, and then to plug in power and power it up?
(this is to essentially re-seat the drives before powering back up, just to make sure there wasnt a loose/intermittent connection)
another thing you could try, but only when no other rebuilds are taking place and only when the drobo is in a stable state, could be to try putting the drobo into readonnly mode, for example as mentioned here, to see if it lets you access the data for longer, before doing any more rebuilds?
(it might, if you can, be worth making a backup of the data while you have access to it, just in case, and then depending on whether it is the unit, or the drives, yes it may be worth getting another, newer unit, that you could upgrade into, ,via a migration process mentioned here: http://www.drobo.com/resource-center/migration/
or possibly a newer unit plus newer drives, which may also help with better compatibility for your computer too)