Hello Ustitan,
Please help me understand if you have tried running the Pre-Boot System Assessment (PSA / ePSA) Diagnostics. If not, run the test and check if gives any error code. Note down the error code and update me with the same, would let you know the next course of action.
I would also like to know what exactly do you see on the screen when you turn on the computer. Are you able to boot the system into Safe Mode? To boot into Safe Mode, restart the computer and keep tapping F8 key at the Dell logo screen. Once the computer enters Advanced Boot Option, select Safe Mode. Press Enter. Check if the computer is booting into safe mode.
Please write back with results.