double loop until the end (?)

Hi guys
I don't know hot to work with loops and also, don't know how to "find" the last record for the loop as well as sometimes the comand copy paste till the last rec sometimes it works and sometimes don't. Clearly don't know anything...
I've attach the loop if file so you can see what i need:
Sheet 1 : This is the file i have after "worked on it". There are other fields on line 18 besides what you see.
It's suppose to take that bold number, today on cell D19, and copy it till the last record on same column before it stars the other number "020" wich today is in line 43, and so on, till it doesn't find any other number to copy.
Sheet2 : is the result of what i said before on this last paragraph. On this sheet it's supposed to delete all the lines that in column C or D are blank. I don't know why it doesn't result with me. I do control+end and delete. Sometimes it works and others don't.
And that's it.
I hope my english was understandablee.
Many thanks
Best regards
Pedro