How do I find out the quality of systems

Hi,
I recently joined a small company as a systems administrator. I bought about 7 new systems which have been assembled by my vendor. I have problems with those systems which are not even 1 month old. Problems like the system swithcing off all by itself, mouse hanging, slow performance etc…

The system configuration is AMD K6 500, 64 mb ram, 10.2 gb hard disk. Moreover in the system the hard disk capacity is shown as 8 gb or 6 gb at times when the actual capacity is 10.2 gb.

Can someone tell me how to find out if my systems are faulty.

regards
rajesh