I can tell you exactly what this problem is. Do a Google search for "Dell" and "Throttlegate" and you'll be inundated with information from loads of pissed off people.
When first released, the E6400/E6500 (as well as various XPS and Studio models) were notorious for suffering from overheating problems. Dell, instead of fixing the problem, spent lots of time ignoring customers and deleting threads about the issue in their support forums in a futile attempt to make the issue "go away". Some Dell engineers eventually created a BIOS to solve the heat problem. It used a combination of reduced CPU multipliers and Intel's CPU Clock Modulation feature to reduce laptop temperatures. It also had the unfortunate side effect of being so over-sensitive to overheating that it reduced laptop performance down to approximately that of a brick with an LCD attached.
Apparently, you have that BIOS installed in your machine and something happened (probably an overheat) that triggered it.
The first step to fixing it is to update to the most recent BIOS which is available -- Dell allegedly released a BIOS that was supposed to resolve the issue.
If a BIOS update doesn't fix the problem, there is a utility in the following thread you can use to get around it. However, you have to be very careful with it. It works by maximizing the CPU multipliers and disabling CPU clock modulation. When using it, you have to monitor CPU temperatures because the utility will have the side effect of overriding the thermal protection on the laptop (meaning, you can literally burn up your CPU). It also has the side effect of severely reducing battery life when on battery, so don't enable it unless you are doing something beyond web browsing that needs the higher performance levels.
http://www.xtremesystems.org/forums/showthread.php?240717-Dell-Latitude-E6500-E6400-ThrottleGate-Fix
Facebook
Twitter