There's something wrong with the CPU. All my machines and many others I've seen published have a benchmark where the integer is mostly near double the floating point capacity. E.g. my P4 is about 1250 Whetstone and 2500 Dhrystone, WHEN BOINC is the only application loaded. Things like BOINCview and web browsers can depending on the moment in time randomly cause for the benchmark to be lower by a very substantial value.

Whatever the MS System screen tells you is not the actual CPU speed. For that you need a utility like CPU-Z.

Suggest you get ahold of a MS/SysInternals utility called "Process Explorer" as it giveS much greater depth and detail as to what is eating CPU time. Recently noticed with it, that there is an actual thing called Deferred Procedure Call. It is not shown in the regular Taskmanager and can consume between 0.5 and 3% of CPU resource of 1 core. Each process with PE can display a CPU usage graph. It shows usage with 2 decimal precision. Many little ones add up.

A drop in performance will cause a drop in points. The benchmark is an indicator, so if that goes down, the claims go down and consequently the credit. Sum the Whet+Dhry-stone values and divide by 480. That gives your approx. hourly claim.

In case you don't find any other cause, try switching your automatic windows update from daily to once a week. I've seen the daily setting have varying impact on different machines, ranging from no impact to totally stopping the Boinc client.