It's an issue with win10 and the g3258 on a non z series motherboard. Win7 and 8/8.1 have optional updates from the windows updates that include one containing microcode from intel. Win10 has it by default and it will allow overclocking if one of the two cores is disabled. They basically 'fixed' overclocking on non overclocking chipsets.
There's supposed to be a workaround. First make sure your bios is set to the default settings (factory settings). Then if you look for C:\Windows\System32\mcupdate_GenuineIntel.dll and rename it to something like C:\Windows\System32\mcupdate_GenuineIntel.dll.BAK (using the BAK as an extension short for 'backup copy') it disables it as a functioning .dll file. Reboot after changing, then you should be able to overclock your g3258 on the h81 board again as you would have before installing win10. Hopefully it works for you.
https://communities.intel.com/thread/77391
Edit: If you're using win10 home it may or may not last long. I don't personally have win10 loaded so I'm not sure which updates are downloaded by default, only critical, all or what. I do know there's no option in win10 home to disable updates, they're mandatory unlike pro or ultimate. If the intel microcode .dll is part of the mandatory updates then the next time win10 home automatically updates it may re-add that bit of microcode and interfere with your overclock in which case you'd have to reset the bios back to default. Intel is addressing the issue that boards with chipsets other than the z series (z87/97/170) weren't officially intended for overclocking.