I have a following code:
OleDbConnection aConnection = new
OleDbConnection(\"Provider=Microsoft.ACE.OLEDB.12.0;
Password is a reserved word in Access so you need to wrap the password column in square brackets in your query. You also need to wrap the columns you're inserting data into in parentheses:
INSERT INTO (Client cname,phone,[password]) VALUES(...
As @HarveySpecter points out in the comments you should also use a parameterized query rather than concatenating user input otherwise you're opening yourself up to SQL injection attacks.