One bad hdd can lock up a system, unplug your slave or second hdd and run your computer for a while to find out if that is your problem. If your master is going bad you will have to image your system to a known good hdd using Powerquest Drive Image or Norton Ghost before you lose everything. I have had hard drives spin down and then not want to start up and hang the entire system.
Since you think one of your Maxtors is going bad you can use the Powermax diagnostic utility found on the Maxtor disk you got with the hdd or download it from the Maxtor site.