Hi Mate,
Even I faced the same issue on my VAIO SVF15318SNW after upgrading it to Windows 8.1
I turned the internet upside down to find any relevant clues to find what caused this problem.
The suggestions answered were quite normal but no one has guaranteed it would fix the issue.
I had fixed mine on my own, please go through it to check if that helps on your model too according to win 8.1:
1. Run MSCONFIG --> Services Tab -->check "Hide all microsoft services" -->now uncheck any update related service or unwanted applications like UTORRENT, ADOBE that have a service running during the startup. However after boot if you open the app, the service will start automatically
2. Turn off the Microsoft Search Indexer service that grabs most of the processing.
3. Go to --> Startup Tab, it will say to open task manager.
Disable all of the third party softwares that start during the boot.
4. Proceed only if you require hibernation mode enabled -->Open CMD as admin -->
At the command prompt, type powercfg.exe /hibernate on, and then press Enter.
5. : Clear Temp files in the %TEMP% directory --> (Just copy-paste in start)
6. Check & analyse the C: drive disk fragmentation, should not be more than 5%
7. If you are using any antivirus program, I would suggest to switch to a cloud based since it users minimal resources of your laptop.For win 7 I would recommend Microsoft security essentials, else Panda Cloud Antivirus Protection.
8. Keep the battery consumption on balanced mode. If you have Vaio Control Center -->Open--> Turn ON the Battery- you check on the details to check out it's features, I have enabled it on my end to have a longer battery life.
9. Uninstall any unused applications they you don't require very often to free up some diskspace on C
10: Install tuneuputilities to manage basic issues.
Hope this helps!! Cheers