Windows 7: FPS drops in most of my games

Thanks again for responses. I have already changed thermal paste. Before changing thermal paste, temperatures were from 70 to 95°C, but now when I changed it, temperatures, like I said, are from 70 to 80 °C. So, changing thermal paste helped me partly. I am considering to buy a CPU and case coolers, but firstly I want to know where the problem is exactly. Also, I tried the method, which essenbe offered me. I used that program (GPUz) to check my GPU stats and information when playing. All I can say that there, in the GPU stats log, is almost no difference when the game runs smoothly or laggy and with low FPS. GPU fan speed is from 40 to 45% and the temperature is from 40 to 60°C. But when I am playing a game, GPU load is from 90 to 99%. Does this mean something and can affect my games FPS? Like I said in my first post, I think that there can be RAM issue? Maybe bad sectors causing the FPS drops in my games? I think that I need to check my RAMs with program called Memtest86+. Can this program help to me? Anyway, that was my reflections about the problem. It would be great if you, guys, or other could give me more advices and help to resolve this annoying problem. I am looking forward to this thing! Waiting for more helpful advices!

what CPU cooler are you using? The CPU temps are too high. And yes on the memtest, it could show whether you are having errors in your ram. What games are you playing? Intensive games use more ram and you have 4GB with a 64 bit OS. It takes about 1.5Gb just to run the OS. And what about your PSU? It may be helpful if you would fill out your system details in as much detail as possible. In the bottom left of your post you will see system specs, click that and click update system specs. You can look at mine to see what we are looking for. But, for whatever reason, if you are maxing out your GPU, you are going to have drops in FPS. FRAPS will cause that, if you are using it.

Agree with essenbe, your CPU temps are too high, especially if you just re-applied the thermal paste.
Your complete 'System Specs' will help us to further analyze your problems.
Intel® Core™ i5-760 Processor
Tcase is 72.7°C, add 5°C for individual CPU core temp max of 77.7°C. Even with the stock Intel CPU cooler you should be at max in the low 60's.

DAEMON tools is known to cause issues, you should un-install it for testing.

Run memtest86+ for a minimum on 7 full passes with all RAM cards installed, best to run overnight.
Stop the test if you get any errors.
RAM - Test with Memtest86+
If you get any errors follow the steps in the tutorial linked above.

Can you download CPUZ and post a snip of the CPU, Mainboard, Memory, and SPD tabs.
For posting the information , enter 'Snipping tool' in the Start button > Search box, hit enter. Select the area you want to post and save to a convenient place.
How to Post a Screenshot in Seven Forums

Check your CPU core temperatures, this will give us info and help with diagnostics.
Use Real Temp , to check the CPU temps when at idle, under load and/or testing.
Let us know the minimum and maximum temps you get.

Thanks again, guys. You are very helpful! I haven't much time to posting a big reply and I only want to show what I noticed. In the screenshot you can see my GPU log logged by a program GPUz. I noticed that when FPS is low (8-30 FPS) GPU Core Clock is 50.6 Mhz and when FPS is good (55-100 FPS) GPU Core Clock is 405.0 Mhz. I searched in google about this problem a bit, I found out that there can be leaks or problems with my GPU Memory/Core Clock or something like that. This is my quick note about GPU and I don't know if it means something important.
essenbe and Dave76, thanks for advices and suggestions. I will actually answer your questions, post needed screenshots and update my system specs! I will do it soon (probably tomorrow). I just wanted to give a quick note about my GPU. Maybe it's worth something, I don't know.
Also, my PC started to lock down when I don't use it and when it is on idle. Maybe this is related to my problem because yesterday there was no lock downs.
I will update needed information soon. Thanks for the help!