Sleep issues and external hardrives

[elliemiller1989]

I brought a external hard drive with worked fine with my Mac Mini (ran Tiger) but when I use it with my new iMac (Lion), the iMac doesn't wake up from extended periods of sleep and I have to hard reset it. I have owned Macs for 6 years and never had a problem but I'm not that whizzed up with how to fix it.
Really don't want to pay for AppleCare or buy a new hard drive if possible but Im completely confused.

Are there any hard drive makes which cause problems with Lion?

Much much much appreciated

 

[Razorhog]

You might try some google searches on the subject. A quick one produced a thread on the subject here, but I'm not sure how the external hdd comes into the problem: https://discussions.apple.com/thread/3200352?start=0&tstart=0