What was upgraded in your system? Was the operating system, the BIOS, the hardware? Please elaborate.
Did you try a different SATA port and cables or connecting the drive to a different system?
Well I have upgraded the mainboard (I went from intel DK55 board to MSI Z97 G45 Gaming). I have also got new memory moduels (Corsair value series 8gb DDR3 1333 (2x4GB)). Obviously the CPU is now i7 4670k. Rest of my system are the same. In my old system I had also win 8.1 64, same as what I have now.
Yes I have tried with different sata cable and different ports. The problem is the same. I haven't connected the drive to another system tough....I can test it in my laptop later.
I have also noticed when the systems boots (after re-seating the power cable of the ssd drive) it sometimes locks up the windows right on the login page of windows.
Please make sure you have the most recent Drivers and BIOS for your motherboard, they should be available from the manufacturer's website.
Check if the SSD is connected to the first (main) SATA port of the board.
Also, verify if the Storage controller is operating in AHCI mode (SATA), or in IDE mode (legacy).