I can recommend some additional troubleshooting steps you can try.
-You can run the Intel Processor Diagnostic Tool which will run a stress test to the CPU. This is the link to the software http://www.intel.com/support/processors/sb/CS-031726.htm
- You can run hardware tests to other components of the system like Windows Memory Diagnostic tool. You can check if DELL has some other tools that allow you test other components in your computer.
-You can test the system just with the devices it came with. Do not connect USB devices or Hard Drives to the computer.