My PC specs:

Motherboard Name - Gigabyte GA-945PL-S3
CPU Type - DualCore Intel Core 2 Duo E4300, 1800 MHz (9 x 200)
OS - Microsoft Windows 7 Ultimate
OS Kernel Type - 32-bit
OS Version - 6.1.7601

I bougth a new video card one month ago. GeForce 210. I didn't have any problems. I wanted to overclock it, in other words: "Play with it". So I installed Gigabyte EasyBoost from CD and overclocked the GPU 590 + 110 mhz, memory to max to 960mhz from 800mhz. Benchmarks showed a little bit bigger score. Then I overclocked shader clock from 1405 to [..] (don't remeber really). So I was playing Modern Warfare 2 when off sudden computer froze when I wanted to select team, I was afk before that. I had to reset CMOS. After that I had problems with Skype: unread messages and no sound. Then I figured it out that when ever I open EasyBoost - Skype starts to glitch again. Now I use EVGA Precission X.

Now after a month, I cleaned computer and closed the case, it was open all the time. I started to overclock GPU clock only (just a bit) because there was no problems that would stop me. So sometimes on heavy CPU load graphics starts to lag. Dragging a window is painful to watch too. Sometimes the screen freezes for 5 to 10 seconds (I can see that hard disk activity is maximal). You may say that CPU fault it is, isn't it? But sometimes lag spikes starts randomly when CPU load is at maximum.

All 3 benchmark softwares (PerformanceTest, NovaBench and MSI Kombustor) shows that performance of my video card has dropped about 25%. BUT! CPU score is lower too.

I ignored these problems but when I refreshed Windows Experience Index I was shocked.

Month before (in latvian language but not so hard to understand):

Now 01.04.2012 (upgraded RAM):

This happened when I tried to capture Minecraft with Fraps on underclocked GPU to 580mhz (def: 590mhz):

All drivers are up to date. Average CPU temperature from 55°C to 75°C (at 70°C sometimes starts these lag spikes). Video card's tempratures are from 45°C to 60°C (very hard to reach 60°C). So my hope is that the video card is fine, cause this card is very new and I want to upgrade CPU anyways. Aplogies for my mistakes in vocabulary (I am trying to type this as fast I can).

Update 02.04.2012 - 7:21
Forgot one thing, my hard disk is extrimly slow and I will upgrade it this week or next week so I will be installing same OS again. I am multi-tasker but I can't do much because of 1.8 GHz CPU and slow hard drive (Model ID - WDC WD800JD-60JRC0).
The Windows Experience Index is back to normal. Actually "Spelu grafika" (Gaming graphics) are higher than month ago. During this test mouse was very lagy, but month ago there weren't any problems. WHY!?