Is this the sql 'ERROR' log or the sql 'TRANSACTION' log?

SQL Error log

you can cycle the error log so it will create a new one with the following command

Exec Sp_Cycle_Errorlog

I don't know of a program that would allow you to open a 35 gb file to see WHAT has caused it to grow to 35 gb's...if it is an active issue or something in the past...

When is the last time the sql service was stopped and started?

If you were to choose to cycle the error log and remove that large file I would closely monitor the new error log to see what you have going on with the server.

If the SQL Transaction log is too large and has filled the drive you could backup the transaction log to clear it and then shrink down the physical log file to an appropriate size and set a growth limit to the file so it won't fill the drive again...I would follow that up with an alert for a full log.

If you simply cannot wait for a log backup to complete on a 35 gb log...then switch it from FULL recovery to SIMPLE recovery...and re-run a FULL / differential backup immediately to restart the log chain.