[CentOS] YUM and RPM often freezes my computer

Sometimes when I attempt a YUM install, it will get to the point where 
it is looking for packages to install, and my hard drive will make a lot 
of noise, but there is no progress. My mouse cursor freezes, and I can 
not switch between programs or kill the process. Eventually I have to 
reset the computer in order to get control back.

The same thing will also happen when I install an RPM. When it checks 
for dependancies, it will freeze up my computer in the same way.

This happens about 50% of the time.

However, after resetting and rebooting the computer, if I attempt the 
same install again, it will work fine.

Also, this may or may not be related, but in the case of YUM, when it's 
installing multiple RPMS, sometimes it will install only some of them, 
and then stop, without any explanation. If I repeat the install, then it 
will install the remaining packages, and complete the process.

Any possible explanations for this behaviour?

Dave