small glitches and freezes could be just about anything - but repetitive noot errors are most likely to be ahrd drive or RAM errors.
You can download a RAM test program for example click here
You can also download programs to test the hard drive, for Maxtor it's PowerMax at click here
Be VERY careful about running some facilities, which will erase all the information on the drive.
Tjere are also other things which could cause your problems - such as the motherboard, or processor, or PSU, or simply bad connections where items are plugged in - but less likely.
Unfortunately the only way to troubleshoot where the real problem lies is a long process of trial and error. You might strike lucky on the first thing you try - you might not.