"can I cash the check into my personal account and deposit the money later into the new institution within the allowed 60 days window?"
Technically, no. The fact that no taxes are being withheld implies a direct rollover and the check should actually be made out to the receiving account, not just to the financial institution FBO you. Still, 401(k) plans often make the payee ambiguous such that it is possible to deposit the funds into any of your accounts at that financial institution, and depositing the funds into a nonqualified account does cause the distribution to fail to be a direct rollover despite no taxes being withheld. Since the distribution fails to be a direct rollover, completion of the rollover would have to be accomplished indirectly by the 60th day following the date of the distribution. You certainly can't deposit the funds into any account at a different financial institution because neither you nor that different financial institution is the payee on the check.
