DELETE is not responding, Don;t know what is going under the hood

Hi Forum,

I have a Table 'customer' with 1000 of rows and around 20 columns. I am trying to delete a row with custnum = 10 but looks like it is executing forever. I did wait for 10 minutes before killing the DELETE operation in SSMS. My Table has no clustered index. Following is the DELETE statement that I am running

DELETE customer where custnum = 10.

Previous to this operation I had a unique index on custnum field, but for an experimentation purpose, I deleted the unique index and added one more row with custnum 10.

But it is not only custnum = 10, where DELETE is not responding, even for other custnum values, DELETE operation is not responding. I am not sure, what is going wrong. For Other Tables DELETE is working fine.

Please help me understand, what SQL Server is doing here.

Thanks