Could anyone please tell me what am I doing wrong on my 4 computers, since I am able to crunch only one task at a time on each of them?
It looks like your preferences are set to use all available CPU cores for a single LLR task.
How many cores do you want used per task? You set this in your "edit preferences" page under the "job control and multi-threading" section. The second option ("Max # of threads per task") should be set to how many cores you want each task to use.
For example, your tasks on this host are currently running using 35 threads.