Resolved PC reboots randomly, no error messages

I have an Alienware X51 R3 32gb ram, Nvidia GTX970 4gb, i7 3.2 ghz.
As said in title, I'll be playing a game, or sometimes just working on it and it reboots. No messages either before or after.
I looked at Speccy and there are no errors there.

 

Have you over-clocked your comp?
Are your RAM matched?
Is your PSU in good order?
Are all your comp connectors seated firmly?

 

Thank you for the quick reply!
No, never overclocked it.
I replaced the memory about 3 weeks ago with 2 16gb sticks. The problem started about 3 days ago.
I'll pull the cover off and make sure everything is seated.
I'm not having any other issues besides this. Is there a way to see if it's the power supply?

 

Your PSU would have to be tested by a Technician with the appropriate test gear. Otherwise can you get a loan of a good one to try and ascertain if the comp works OK.
Are the memory sticks all matched?
If you replaced the RAM 3 weeks ago and the trouble has developed since that time, you may have loosened a connection while carrying out the job.
As always make sure the AC Power is off and beware of ESD's. (earfh yourself)

 

If you still have the other ram, put it back in. If you have 2 sticks of ram, remove one and see what happens. If removing one and it still happens, replace it with the other stick to see what happens.

 

Yes, the memory are both the same; Corsair Vengeance LPX DDR4 2133MHz. Came in a two pack.

 

https://www.dell.com/community/Alie.../Alienware-X51-R2-Random-Reboots/td-p/5615921
I had a look at the specs which quoted a PSU 330W.
Googling found the link above which suggests a need for more power as by todays norm, 330Watts is looow.

 

I'm not sure what it is. A friend from work gave me the computer. I've opened the case but the power supply and graphics card are behind a big metal plate. I don't want to fiddle with it as I'm not sure I can get it back on.
I did open the case and reset the memory sticks and also unplugged and re-plugged several connectors.
While I had a couple of game crashes, the whole system didn't reboot.

 

Just so we know what we are dealing with. Your comp is a gaming unit?
The specs I Googled indicated that and the link also dealt with gamers who said the unit was borderline powered with a 330 Watt PSU.
You had no problems before adding the extra 16 GB's of RAM?
This may have been the tipping point for giving you the Restarts.
I would remove the extra RAM and try it as it was standard when you bought it to see if you experience any Random Restarts again.
From what you say about location of the PSU, I would suspect it may be a dedicated unit produced for Dell and is OK for the load they built into it.
These dedicated units (HP do the same) will not allow a change to a normal ATX size PSU.
I once had to cut the comp case to enable me to change out the faulty PSU and install a Standard PSU. (HP)
Fixed my problem at the time as I went from a 280 W PSU to a 400W unit.
Let's know how you get on.

 

I've been testing the computer quite a bit and after I reset the memory and cables, I haven't had the issue. I've tried several different games, playing each for a few hours at a time, and no reboots.
Once I'm able to go out again, I'm going to look into getting another PSU.
Thank you for all your help!

 

Does this mean you removed the extra RAM you put in?

 

Sorry this took so long to reply. Yes, I did remove the new memory and replaced the old. It worked fine for a while but had the issue again. I'm playing a game, when suddenly it freezes, and the monitor shuts off like I shut down. The light is still on the PC but nothing else. task manager doesn't open, nothing. I have to hold the power button down to shut off the computer.
I also just hooked up my graphics amplifier again and it works. It had suddenly stopped, at least the PC no longer recognized the card in it (GTX 980 Ti).
I just got it all set up again and it's working. I'm hoping this will solve any power issues I have as the card has its own dedicated power supply in the amplifier.