My SSD freezes after booting

Hi,
I am using Dell workstation T-7500 with Win-7. I use 500GB SSD as my boot drive & others 3TBs 3 of them as storage. I have been using this PC for over 10 years. Today I was working & downloaded some stock market data which I do every Saturday. After that I connected 3, 3TB HDD SATA III drives to back up this data & rebooted the PC. But then it boots ok but I can not open any files, folders, websites etc. So I tried rebooting several times & came across same problem.
So put a cloned HDD & put SSD as a slave drive & found the same problem with the HDD too.
So I changed the SATA Cable & that too did not help.
Then I put the SSD in 2nd SATA slot & it didn't work. All these times I disconnected 3 TB HDD for elimination process. Nothing worked. Finally I put just the cloned HDD in 2nd slot which I use to cone SSD to HDD & it didn't work so by this time I was frusted & had something to eat. Then all of a sudden that HDD in 2nd slot all of a sudden worked.
So I replaced it by SSD which had the downloaded data & connected one 3 TB HDD to back up data as fast as I can which I did. Now I am scared to shut down the PC & connect rest of the HDDs ( 3 x 3TB HDDs & a 500 GB HDD to clone this SSD so that I will have backed up data & a new Cloned HDD in case something goes wrong.
But before I do that I thought I better take advice from experts on this forum in case I run into same problem.
My room has A/C running so that eliminates probably overheating.

Please advice.

Thank You

Please edit your profile with ALL your hardware specs. It will help us to help you
System Info - See Your System Specs

Have seen this on an old computer.
Shut down, unplug the power cord, open the case, remove the memory sticks and gently clean the contacts. If you have a contact cleaner, spray on the memory slots.
When was the last time you changed the CMOS coin battery (CR2032)?

Thank you for your suggestions.
Don't know how & why but after an hour or so it started working by itself.
Can't remember when I changed the CMOS battery so must be long time ago.
How often should I change it ?

When the CMOS battery is gone you will loose the BIOS configuration settings and the clock is reset to years ago.
Most desktops has a CMOS voltage sensor.
You can see it with HWiNFO.
Extract and run.
Select Sensors and look for Vbat. New is abour 3.3V Replace if below 3.0V