Over clocking issues

I'm not sure if this is the correct place to ask about this but whatever

I recently bought an i5-2500k and this motherboard. Overclocking it seemed simple enough, you just changed the multiplyer in the bios and bam I got the i5 up to 4.5 ghz acording to cpuz. But after my computer has been on for a while the overclock stops working and I go back down to the stock speed of 3.4 ghz (with turbo) so I was wondering if I had done it wrong or somethingm or any possible solution

I don't exactly need the performance to be honest, but I paid more for this stuff so I naturally want it too work...