It goes to sleep and i cannot wake it without a hard shutdown/ start . it is a Aspire 5336-2634

Go to 'Start'--->Programs--->Accessories--->System Tools--->System Restore

Here you will have to check "Restore computer to an earlier time' and click Next
Now you will find one Month Calendar window with Dates below, go to the previous month by clicking the '<' sign in the upper left hand corner of the Month Calendar and select any date that you see in Bold.

The detail of that particular date should show "System Checkpoint" and time on the right hand side box. Select that date.

Now, Click on Next and System Restore will start and windows will take a reboot.

Go to 'Start' and then Run
write "msconfig" inside Run tab and press 'enter'
inside the 'System configuration utility' window click on 'startup' tab then uncheck all the applications except your current antivirus and press apply then 'ok' and then 'exit without restart' option.

Now right click My Computer and go to properties tab.
click 'Advanced' tab then under performance menu click on 'settings'
go to 'Advanced' click on 'change' and increase your virtual memory to 2048 in both spaces.
Now restart windows.

Just do the following steps and your issue will be resolved.

1) Delete all unwanted data from Drive C.

2) Delete all data that you have copied from Drive C to External HDD

3) Open My computer and go to Tools---> Folder Options---->Click on View Tab----> Check 'Show hidden files and folders' and select OK.

4) Go to C:\Documents and Settings\Administrator\Local Settings\Temp and Delete everything that you see inside Temp Folder

5) Go to C:\WINDOWS\ here you will find folders like $hf_mig$, here you will have to Delete all the folders starting and ending with $ sign.

6) Empty Recycle bin and restart the PC and your issue will be resolved.

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Thanks.