fan- the processor fan failed to respond correctly

Is that while running on battery, or with power adapter plugged in, or both?

@RoHe​ when the power adapter is plug in and when running on battery, on rebooting it directly goes to the testing and then it says thermal fan failled to respond 

@haroon92​  - Is this a Vostro 3491?

Appears you have a hardware issue. You probably need to get that checked out before you can deal with the booting issue...

There are instructions to remove/replace the Vostro 3491 fan in the Service Manual, assuming that's your model.  If PC is still under warranty, contact Dell Tech Support for assistance. 

Otherwise, if you can't DIY, you may have to take it to a reliable PC repair shop to replace the fan. If in USA, you can contact Dell Spare Parts (1-800-357-3355) to buy the fan or look on the web to see if any site has the exact Dell fan for sale.

@RoHe​ no it's vostro 3500 core i7 

@haroon92 - Do you have the old Vostro 3500 which reached End Of Life (EOL), or the newer Vostro 3500?

Either way, and assuming PC's warranty has expired,, you may have to buy and replace the fan to get PC to boot.  In USA, you can contact Dell Spare Parts (1-800-357-3355). Have Service Tag available (don't post it here). Or shop elsewhere online to buy a replacement for your exact PC model.  

If you can't DIY, you can contact Dell Out-Of-Warranty Repair in USA for assistance or take it into a reputable PC shop.