Hi @YuliyT welcome to this free user to user Alienware laptop discussion forum. This is not Dell Support. 

Good to see that older systems are still being used. Did not find Product Support for Alienware M18 notebook, it might be M18x (R1) or M18x R2. 

There is a thermistor in temperature controlled dc fans that typically have four wire connections. The fix is to replace the fan(s), having consulted manufacturers label, sticker in middle of fan. 

Thank you for your answer.

Considering fans, I did not mention, that I already cleaned them both and also swaped left one with right one since they are identical just in case. All software do show temperature for GPU and CPU and temperature range seems fine(CPU never over 70, GPU around 80). Today it did not just freeze but hang system to blue screen. Considering all this and fact that few years ago I did replace one of GPUs I'd still blame GPU and I'm going to remove primary one and replace it with secondary. SLI is quite pointless thing this days, notebook works just fine with just one GPU.

Thank you for sharing update. What did Blue Screen say? 

I did not read bsod text, sorry. Anyway, today I completely dissasembled this thing, GPU1 got completely removed and replaced with GPU2. GPU1 fan replaced with GPU2 fan. Did not help, but what I discovered by accidentaly unplugging wrong fan that all issue is caused by GPU1 fan. System works just fine without PGU1 fan(well it heats but do not freeze etc) So I conclude that most likely it must be GPU1 fan controller issue, that thing I can not repair myself nor I think any servicecenter can find parts and replacing whole motherboard for 8 year old computer is not reasonable, alas alienware your time has come. 

Update, YuliyT has the 2013 18 R1.

I'm having this EXACT same issue on my Alienware 17 R1. Two years ago I upgraded it to a 980m and everything's been working fine since. I moded the latest Nvidia driver last week and things worked fine for about a week, then the fans seemingly stopped working in the middle of a game and the machine crashed.

Initially I repasted, but that didn't work. I then read it might be a vBIOS issue, and flashed it a few times and nothing really happened. 

The card works fine and the fans work great during diagnostic mode, I just can't get them to engage.

So you're saying the thing to do is replace the GPU fan?

Hi @YuliyT  parts-people has Alienware 18 R1 Graphics Card Cooling Fan/Heatsink R7H03 (parts-people.com) Internet search also reveals Dell Part Number (DP/N) R7H03 available. 

See removing video fan on page 31 and/or page 32 of Alienware 18 Owner's Manual (dell.com) 

Kudos (thank you) to @DELL-Chris M for clarification system is Alienware 18 (R1). 

Hi @pgaaanj214 welcome to this free user to user Alienware laptop discussion forum. This is not Dell Support. 

Your Alienware 17 (R1) post seems to have supplied the root cause as moded the latest Nvidia driver. Can system roll back these changes to the last good restore point? How to use System Restore on Windows 10 | Windows Central 

The 980m won't work in the 17 R1 without modding the driver. I don't have the previous version I was using available because my hard drive crashed.

Looking at the forums right now, there's 3 posts about laptops from that generation having the same issue so it must be a problem with the new drivers. I'm going to try to mod an older version of the drivers and see how that works. 

I found that if i remove gpu fan1 whole freeze thing does not happen, but I did not put any workload into gpu as I dont want it fryed, so it might be fan, it might be fan controller or it might be some powersupply issue, i dont know. If you want to do same test I did and unplug gpu fan be VERY carefull  temperate rises there in a matter of seconds, my note is old and I did that at my own risk.

Anyway I did submit that notebook to repaircenter, they are still to test it. I will post what they find here, but this is going to take few days.