Why can't I overclock my CPU further?

[Chrizy_D.uk]

OK I have a Celeron 2Ghz on an Abit AI7 (multiplier x20). Crap i know.
Until now I had it clocked up to 2.75Ghz, but since getting knew PC3200 memory i thought i'd try and push it further.
However, every time i try it either hangs in the Bios, or if i try and do it in Windows, it reboots.
How come it won't go any further? I know it's not the memory, and the temp never goes above 60 degrees, with a stock cooler. Do i need to up the voltage? If so what is a 'safe' level for that chip, which has its stock at 1.525V?

 

[GAMEfreak]

read about memory dividers in the stickies in the overclocking thread. please read all stickies before asking anymore questions about overclocking. it saves us time, and you mucking up your pc by mistake. if you have anymore questions, feel free to post here though.

 

[TaKeN]

I would say it sounds like the memory is topping out, we need more info tbh,

Like FSB Speed.
Multiplier Settings
What Speed RAM Is @ Etc.

 

[Chrizy_D.uk]

As I said, I'm pretty sure it's not the memory (unless it has a problem)
I have the memory divider at 4:3 (Mem:FSB), and the FSB at 140, giving the memory a speed of 186 (effective being 373, way short of 400).
I currently have the timings tightened a bit at 2.5-3-2-6, but when I tried clocking the FSB up further I set them back to stock (2.5-3-3-8).
That leaves the CPU at 2.8Ghz, which is a pretty high overclock (40%). Yet the temperature is only 52 degrees at the moment, and that is on full load.

Could it be that the CPU is at its limit?

Thanks for your help.

 

[Mikey1280]

Wel it sounds like your CPU has hit its limit on the stock voltage,I would try upping the voltage a bit more to about 1.6V if you have a good cooler