Was there anything new (software, hardware, malware, error messages) that occurred right before the freezing started?
Software, hardware, malware, or a combination could all contribute to this problem.
Your Dell has onboard diagnostics to check the hardware. Unless you strongly suspect malware, I would start with the hardware diagnostics. Here is your Dell™ XPS™ 420
manual in PDF format.
- Arrow down to page 87 - Starting Dell Diagnostics From Your Hard Drive.
- At the Dell Diagnostics Main Menu, select Test System and then Extended test (Note: this could take several hours)
- If a problem is encountered during a test, a message appears with an error code and a description of the problem. Write down the error code and problem description.
If all hardware passes, we can proceed with other troubleshooting.