The hydrogen of OH groups is in general an exchangeable hydrogen. You may observe these resonances only using perfectly dry deuterated solvents. You should also set an appropriate spectral width since several OH groups could give very deshielded signals, depending on their chemical nature.

Thank you for your answer. I have used deuterated chloroform for the analysis.

Can you please tell me how can I calculate number of OH groups per molecule from H NMR?

In general OH protons give broad singlets and someone expert in structure elucidation may easily recognize them but to have a confirm there are at least two choice. The first, run a bidimensional HSQC: protons without correlations with carbons belong to OH groups (if there are not other functional groups in your molecule with exchangeable hydrogen, i.e. NH or NH2). The second, run a first proton spectrum in deuterated chloroform then add some drops of D2O to your sample directly in the tube and shake, wait for the separation of the two phases and re-run proton spectrum: the disappeared resonances belong to exchangeable hydrogens (OH, if not present other function with labile hydrogens).

Drying CDCl3 prior to use by runing it trough small plug of dry K2CO3 in pasteur pipette can help in observing an OH group. Also consider the use of some other solvent in which exchange of protons is slow (DMSO, acetone-d6)

Obviously, prior to solubilize your sample you should be sure that it does not contain any trace of moisture.

If you are using chloroform, it is difficult to observe some OH and NH group because these are exchangeable proton. If you want to count the chemically equivalent OH, please use deuteriated DMSO/Acetone as solvent. Then go for 1D nmr and then 2D.