Well according to Intel {Pentium® D Processor 830} ->
http://ark.intel.com/Product.aspx?id=27513 has SpeedStep listed as option?!
The next thing is the BIOS version, F2 is required {rev 1 & 2 of your MOBO} for your CPU and IF you're only running F1 then a couple things: 1. CPU has been dummied-down all this time, 2. BIOS will not offer CPU options because the CPUID information is/has been missing. If running F1 then you must flash your BIOS; use the Q-Flash method and a FAT-32 USB off one of the MOBO's rear USB ports.
CPU list ->
http://www.gigabyte.us/support-downloads/cpu-support-popup.aspx?pid=2629
GA-P35-DS3L (rev. 2.0) -> http://www.gigabyte.us/products/product-page.aspx?pid=2629#
GA-P35-DS3L (rev. 1.0) -> http://www.gigabyte.us/products/product-page.aspx?pid=2599#
If you have BIOS F2 or later then refer to page 29 for the Clear CMOS procedure. This will accomplish setting everything to defaults and perhaps repair the problem. Afterwards Load Optimized Defaults and set the Date & Time.