Try using a product like SpaceMonger to find what is taking the most space.
If your database use the c: drive for data and transaction logs you might consider moving one or both.
Hope this helps.
I think the C drive contains the system Databases , Users and Program files .
So I have to move the users folder for example to another partition ? or what ?
I'm actually don't have experience in SQL servers
I am not the best teacher, however you might try the following to show where the databases are located:
SELECT DB_Name(R1.database_id) AS DatabaseName,
R1.physical_name AS DatabaseFile, L1.physical_name AS LogFile
FROM sys.master_files R1
INNER JOIN sys.master_files L1 ON R1.database_id = L1.database_id AND L1.[type] = 1
WHERE R1.[type] = 0;
As for the old stack and crash dumps as well as the Windows Events and Error logs, you'll need to look those up, as well, because there's just too much to post on a forum post.