lion start up problems

I recently downloaded Lion and almost immediately began to have start up issues. When the log in screen appears I am unable to open the system. This usually occurs after the machine comes out of sleep mode. The only alternative I have found is to hold the on/off button and then restart. In some cases, even after the restart, the machine idles for an unusually long time before it boots up!

I have seen references to this issue elsewhere, but when I put the question to a search on this Forum, nothing came up.

Thanks,

Bill