I was about to update here but forgot. Sorry.
So I have finally fixed my PC. Took sometime. Bought new WD HDD as suggested by whitestar above.
I struggled alot to get a bootable Win10. First I installed Ubuntu and then used this guide to create a Win10 bootable pendrive
Make a bootable Windows USB from Linux · One Transistor
First read the guide and then proceed otherwise you might face some difficulties like a faced.
After that I installed Win10, which was also great pain as I didn't know I could create only 4 primary partitions on a HDD. Since Ubuntu was already on primary partitions, I couldn't allocate windows partition/drives as I wanted.
Installed Win10 with 2 partitions, then changed other drive to logical and then created other rest of the partitions, with the help of EaseUs partition manager free, I usually keep. This all was after some hit and trial method
Since I knew I will lose Ubuntu cause of Win10, I deleted it while installing Win10. I again installed Ubuntu though.
So, important thing, did I lose my data? No! Yay! I ordered external case for the HDD, Orico, link is above in posts. Connected and transferred important data to my External HDD, speed was decent 29Mbps which I usually get with any other external HDD. The old HDD which created this whole mess was working fine too, I didn't face any transfer problem while copying data, loading was delayed in win explorer though, may be cause it's a 1TB HDD with 4 partitions. I am not sure.
I remember correctly, I have transferred files on USB 3 with around 90Mbps transfer speed with my friend's external HDD . Don't know why I am not getting it now. May be I need a large file, probably 5GB+.
Anyway, thanks alot for all the help and suggestions. Especially to
@whitestar_999.