The list of ePSA error codes can be found on this Dell support page. According to that page the error code is caused by multiple memory DIMMs failed, presumed to be caused by motherboard issues. Try reseating the RAM modules first. If that does not help then try one RAM at a time. It may be a BIOS problem or the MB may be the cause. Have you replaced any RAM modules before the problem started? As far as the BIOS is concerned, you have a rather old system that Dell has marked as end of life. There are 2 BIOS versions available after A12 that would be A14 and A16. Also considering the age of the system it may also be that the CMOS battery needs to be replaced. But that is a bit of a teardown procedure. Have you noticed any other problems such as the time and/or date is wrong? Or possibly that the system was not always booting into Windows because the HDD/SSD was not detected?
In preboot assessment test, I am facing error code 2000-0261. On searching through ePSA manual I found I should update BIOS and then retry the test. But I have seen some discussions which say bios update is never a real requirement. ( [URL]#M41718 ) Also I read guides on updating BIOS (.[URL]#Creating%20a%20USB%20Bootable%20Storage%20Device )and it seems systems shipped before 2015 don't really have well supported method. Also I am using only linux system which was not shipped with linux. So I feel I Iie on the least favourable condition.  Few more questions I do have is that since one needs to update their BIOS only in stages by stages with every update, so what is next version just after A12?
Do I really need BIOS Update? Inspiron 3521