external hard drive shows on Mac but not PC

It is a mac formatted externaldrive, windows does not understand hfs+ filesystem

Perhaps this is why the teacher asked you to look at it?
Waa it the teacher's or was it given and the data can not be accesses.

In windows, does it say the partition is raw in disk management?

Partition corruption?

Backup the files when accessed on the mac.

Does the enclosure have an external power or it draws power via USB?

Perhaps the HP is newer and not providing enough power over usb ....

the teachers always uses this on his pc and it usually works fine until yesterday it giving this error

Can ypu see what disk manager says about the type of partition this drive has?

it is not showing on disk management

Best advice get the data off the harddrive onto a new one that works.
Just in case.

Does the external support a supplemental power source or has  its own or does it draw power via/from the USB port?

What does the mac say about the fileaystem?

mac says it is NTFS file system. it connects via usb

I find it strange how it works great on Mac with no issues but can't work on a PC

It means there's disk corruption.  Windows loads NTFS differently than Mac.  It's time to copy the files off the system and put it on another drive.  Can you assign a drive letter when you plug it onto a Windows system?

no I can't assign a drive letter

Does the enclosure have a supplemental power source.
Newer windows systems lowered the power that can be drawn through usb 3.0 ports
Usb port C provides a higher power on the port.

The mac you are connecting via a powered USB hub or directly via a mac's usb port?

it's via powered usb hub cause my iMac only has usb c and no usb a..... could that be the reason why it works on my Mac ? it is getting usb c power ?

Possibly. The windows system new 1 or two years old?

Check the enclosure power requirement and then see whether .

The other option, at times they had a USB with a host Ytype USB one solely for supplemental power ( red/black power without the middle usb signal lines

Is this a usb 2 or 3 external enclosure?

usb 3

Check the external enclosure for.power spec.

It might be aging drive needing. More to speed up.

See if something like this can get the drive seen and recognized in a win system

USB 3.0 Cable Dual Power Charge Cables Y Adapter Type A Lead Male to Female Extension Code 30cm (5Gbps Data Transfer and Charging) https://a.co/d/dWduSS3

What pc model do you have here?  
does it have usb 2 or 3 ports?  try using back and front ports ( for desktop)

I suggest that you stop messing with the disk on the windows system.  Get another disk and copy the files to it while plugged in on the Mac.  Give him back both disks.  The disk is failing or corrupt.  If it's just corrupt, then it needs a reformat.  Data should be backed up.

Everyone needs at least 2 disks with all their data.  I actually have 4 for my own data, because I've seen people lose data too often.  You can never have too many backups.

so if I do a reformat the problem should be fixed on windows or it seems this hard drive is not very reliable as a backup

Much depends on whether the issue with windows is a possible NTFS corruption or whether it lacks the power to spin-up the drive.
I gather, in windows the USB2SATA adapter functions, gets power and presents to windows as a USB adapter plugged in, but the drive behind it is not presented.

is the enclosure sealed, or it is modular meaning you can pull the drive out and use another.

I believe is sealed. another thing i noticrd is is blinks white when plugged in to windows but blinks blue when plugged in to MAC

It was working before.  I suggest getting a different disk and copying that data off first before doing anything else.  If the disk works after a reformat, then it's some sort of data sector corruption that Windows can't overcome, but Mac uses it's own NTFS drivers and maybe is bypassing the error.

It's time to stop messing with it until you get the replacement disk.  You can figure out whether it's that disk that's failing or if it's just some sector corruption after that backup is made.

If interpreting your light
white means power, blue means DISK access.

Sealed, the newer enclosures have seamless type (it might be opened with the drive ...

get the data off. since it is a backup, you never when Murphy's Law will come around the bend.

Can you take the Mac's USB hub, and use it on the windows system?

the mac hub is a usb c connection and my windows don't have usb c

i assume it is a seagate disk?  if so, try with another USB cable also

you may wish to post what the disk manager states as arnold asked. it is pointless to go around guessing without first using avaulable debug information.