Have to considered using os performance monitoring tools when u face this problem? This should help u to assess the performance of u'r database & also if u are running short of system resources.

Tools such as
sar -u 5 5 (reports CPU utilization)
sar -r 5 5 (reports memory utilization)
sar -w 5 5 (to check for swapping)
swap -l (swap space usage)
mpstat (statistics per processor)
iostat 5 5(disk activity)
sar -p 10 10(paging activity)

With regards.