Windows Crashes & restarts itself but no message

Hi,
I have Dell workstation with following specs :
CPU : Xeon E5645
RAM : 12 GB
GPUs ; Three AMD FirePro 2460 Low Profile Cards ( To run 12 Monitors )
12 Dell Monitors ( 1920x1200 )
Windows - 7

I have been using this system for last 10 years with no problem. Reason for Win-7 is that System & Cards won't run Win-10.
Recently one Fan that sucks the air & throws inside the system was making noise but system never crashed.
I cleaned the system with a blower & took out dirt. Now it makes much less noise.

But it crashes 1 to 3 times a day & restarts itself & takes much longer 10 to 20 minutes to boot.
There is no message when restarting like graphics drivers crashed or dumping memory etc.

System is in an A/C room ( keeping temp at 86 degree F )

Can you please tell me :

(1) what is causing windows to crash &
(2) why is it taking so long boot &
(3) What should I do ?

Thank You

Have you tried sevenforums?

Scott said:

Have you tried sevenforums?

Click to expand...

No I haven't but now I will. Thank you.