Hello again...
Test your RAM modules and HDD since you got that from your old PC...
You can test RAM with MemTest86+, here is link:
http://www.memtest.org/
If you have more then one module, test it separatelly...
Before testing, clean contacts with rubber and DIMM slots with brush...
Check what make/model is HDD and download testing tools from manufacturers Web Site...
test it for possible bad sectors...
You can use MHDD, it is an excellent tool and it is free:
http://hddguru.com/content/en/software/2005.10.02-MHDD/
I would try with different PSU too... Borrow it from a friend and test your PC...
Hope this will help you mate...