remove blank lines

I have joined 2 files. Join command worked fine.
but the result showing extra blank lines. I tried to remove blank spaces by using awk (-- -42 RS= ORS="\n\n" file.txt) and sed (sed '/^ *$/d' file.txt)commands but didn't remove any
Any suggestions plz:D

123 tab .......
......tab .......234
345 tab ........
......tab.........456

The result should be like this
123 tab 234
345 tab 456

what file1 and file2 contains?

Hi
I solved it
nothing wrong with any commands
it's just my MacBook text format problem.
The thing is windows new lines /n and macintosh /r

Windows uses '\r\n'. Unix/Linux uses '\n'.