His source has dried up, the source of his creation has dried up.
He has stopped creating. He has lost the inspiration and ability to create and innovate ("source" here means a well or a spring of water).
("An east wind, the spirit of the Lord, will come from the desert; his source will dry up and his spring will wither; he will plunder the treasure of every precious vessel" - Hosea 13:15).
Translation
Expression (Hebrew)
יָבֵשׁ מְקוֹרוֹ, יָבֵשׁ מְקוֹר יְצִירָתוֹ
Definition (Hebrew)
חָדַל לִיצֹור. אִבֵּד אֶית הַהַשְׁרָאָה וִיכָולְתּוֹ לִיצֹור וּלְחַדֵּשׁ (מָקוֹר מַשְׁמָע בּוֹר אוֹ מַעְיַין מַיִם).
("יָבוֹא קָדִים רוּחַ ה' מִמִּדְבָּר עֹלֶה וְיֵבוֹשׁ מְקוֹרוֹ וְיֶחֱרַב מַעְיָנוֹ הוּא יִשְׁסֶה אוֹצַר כָּל כְּלִי חֶמְדָּה"- הוֹשֵׁעַ יג טוּ).