The best way I found for logging temperatures with free software is using Speedfan. You must enable logging in the settings. Here is a little guide on how to set it to log the various sensors. You are interested in the CPU and MB temperatures, as well as fan speeds.
Speedfan will save the log as a csv file in the executable folder. You can open the file with any text editor or you can import it in Microsoft Excel or OpenOffice Calc to see the data as a table.
You should use a stress test program such as IntelBurnTest. This will ensure that the CPU is running at its maximum power.
To diagnose hard disk problems, you could check the Windows Event Viewer for error messages about HD and controllers, or you could make some tests by copying large files or running a chkdsk /R
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To diagnose PSU problems, I'm afraid the only possibility is to replace it with another PSU and test the system.
Consider that your problem might also be caused by a faulty/damaged motherboard. A damaged disk controller might cause the "disk not found" thing.