Intel Pentium 4 2.6GHz downclocked to 1.8Ghz?

Not long ago I noticed a weird thing on my old computer. When I go to my computer properties it says
this:
And I was like: what the hell does the 1.8 Ghz stand for?
And I realised that games that require 2.4 Ghz cpu were lagging. So I downloaded CPU-Z to see the exact specifications my cpu had, and I saw that my cpu has 1.8 GHz .
Results from CPU-Z:


It says in specification 2.4 Ghz and in core speed 1.8 Ghz. Wtf?
I'm pretty sure its not the power saving feature because even when I stress test it remains 1.8 GHz.
Any Ideas? Was it downclocked? Its a second hand computer so maybe someone downclocked it before?

Sorry for bad English.
Thanks in advance.

EDIT: Sorry I messed up the title it should be 2.4 Ghz and not 2.6 GHz.

What does it say in the BIOS?

You could note the current BIOS settings and then load defaults.

pbcopter said:

What does it say in the BIOS?

You could note the current BIOS settings and then load defaults.

How can I do that? I never used BIOS (except when I was setting the boot device). I found nothing. I checked all the menu-s, haven't found nothing about the CPU except the temperature and fan speed (RPM).

Have you looked at the manual for your motherboard?

Motherboard - P5G41T-M LX3 - ASUS

pbcopter said:

Have you looked at the manual for your motherboard?

Motherboard - P5G41T-M LX3 - ASUS

P5G41T-M LX3 - ASUS is the motherboard of my new PC, my old PC has a different one and I was too lazy to open the casing and see what's the motherboard so I went to see what CPU-Z says:

I searched for that motherboard user manual on the internet for 30 min and I have found nothing. Am I searching incorrectly? Please help!

Thanks in advance!
Sorry for my English.

I found the problem! For some unknown reason windows is saying that I have a Pentium 4 2.4 GHZ . Actually in the BIOS is says that I have a Pentium 4 1.8 GHZ. In the BIOS the CPU voltage, frequency and the multiplier are not changeable. I thought I could change at least the frequency but actually I can't. I can't even lower the multiplier (why would I ever do that but I heard that is the CPU is not unlocked I can at least lower it; just wanted to try). I restored the defaults in the BIOS, saved the settings and guess what, the CPU was still at 1.8 GHZ. I booted in windows successfully but still at 1.8 GHZ . But why does Windows say I have 2.4 GHZ?

However thanks on the reply.
I will mark this as solved.