If your PC is running really slowly and that is not normal then you should try posting in the Am I Infected forum and telling them you have a slow boot up and they will be able to help you diagnose possible programs which are eating up your PCs memory.
Before you go there though you should download the following:
A good antivirus, If you already have one then run a scan
Two good antivirus programs free for non-commercial home use are Avast!
You should only have one antivirus installed at a time. Having more than one antivirus program installed at once is likely to cause conflicts and may well decrease your overall protection as well as impairing the performance of your PC.
A good antispyware. Again, run a scan if you already have one
There are a number of good antispyware programs, adware
, spybot s&d
for a start.
The Am I Infected forum will provide you with other measures to protect and also to sort out any programs which may be causing a problem. Check the "Before you post a query" sub-forum there to find out what else you should do before you post for help.
Good luck and if you want any further clarification of this post then just reply.