As jggimi mentioned, just grab a snapshot kernel for a mirror.. rename the kernel and nove it into /, as bsd.cur for example.
ftp://ftp.openbsd.org/pub/OpenBSD/snapshots/i386/bsd
(Permissions should be root:wheel, 0644.. or.. -rw-r--r--)
jggimi explained this above, at the
boot> prompt, type
boot bsd.cur -s, see if the problem persists.. if it does, reboot and enter the UKC,
boot bsd.cur -cs, disable apm or acpi, whichever was selected automatically the first time.