Not initiated hard drive?

So you have used the Disk Management utility. Open that up again and look carefully at the LOWER RIGHT pane, and scroll it to find your 1.5 TB second drive. The rectangle representing it will have at its left end a small label box with a disk label like "DISK_1", a type like "Basic", a size in GB, and a status like "Online". To the right the rest ought to be divided into three sub-blocks, each representing one of the Partitions. On each Partition should be a set of label data giving you the Volume Name, the letter name in brackets like "(D: )", a size in GB, a File System like NTFS, and a status descriptor. There are two relatively common problems seen here. IF a Partition does NOT have a letter name assigned to it, Windows cannot use it. If that is your situation, RIGHT-click on that Partition and use the menu to assign a letter name not already in use. Then back out of Disk Management and reboot so Windows can update its Registry. You might have to repeat this for other Partitions if they also are missing letter names.

The other more time-consuming problem is when the File System is shown as "RAW". Usually that means there is minor corruption of some of the key system files on that Partition and Windows can't use it. If that is your situation, search the web for ways to recover from a RAW format problem. Many of the solutions involve using software tools to find and copy all your good data to another clean HDD before re-Partitioning the troubled drive.

Good luck. Let us know what you find.

Alright so once again I opened the utility. The supposedly 'BASIC' value is shown as 'UNKNOWN'. Below are 13xxGB and the status 'not initialized'. The most important thing is that the WHOLE drive showed up as one unallocated drive. So I'm guessing a corrupted partition table, and that Windows chkdsk it on every boot slowing down the process. Although Windows never tagged it as RAW I think this leans to the RAW case.

But then there are so many softwares out there, could you recommend some of them? How long would this usually take (scanning for files and recovering them)? Thanks

I can't recommend any particular software because I have never had to do this. BUT I do not think you should approach it as a case of recovering from a RAW format situation. As you say, suspicion is on the Partition Table itself since Windows can't determine the fundamental disk type. You should look instead for a tool that analyzes and fixes the Partition Table. If that can be repaired, the actual File System files on each of the Partitions might be OK. Or at least, you might find that only one of the Partitions has a RAW format problem.

Thanks for your advice, I'll try fixing the partition table later this day. Just to make sure, is it safe for the data to fix the table?

Normally any utility for fixing a Partition Table writes new data ONLY to the Partition Table itself. It does not write to any of the data file areas, and not even to the Directory and FAT areas of any Partition. So you should be OK.