As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN CRUISE FL360 FMC P/RST SWITCH LIGHTS ILLUMINATED AND NO SCRATCHPAD MESSAGE WAS DISPLAYED. LOST BOTH LNAV AND VNAV. CHECKED QRH. REENGAGED LNAV AND VNAV AFTER APPROXIMATELY 2 MINUTES. NO FURTHER FAILURES. ALSO VTK WAS NEVER DISPLAYED. GROUNDED - YES. PERFORMED B737-800 FIM TASK 34-61 TASK 836-NO DEFECTS OR FAULTS FOUND. ALL OPS CHECKS NORMAL. AIRCRAFT OK FOR SERVICE AT THIS TIME.