windows won't boot after installing new theme

Try F8 System Recovery Options as suggested to run Startup Repair. It should automate System File Checker and System Restore, but if not run them manually from the list and Command Prompt: SFC -SCANNOW Run in Command Prompt at Boot

If F8 Repair console is unavailable or these don´t work possibly because of System File corruption or infection, try each from the DVD Repair console or System Repair Disc - Create

If these all fail you may be infected, so boot into Safe Mode to run Malwarebytes, or if this fails download, burn to CD or write to flash stick, boot and do a full scan with Microsoft Standalone System Sweeper.
Then start over with the Repair steps if necessary after cleaning up any infection.

If this fails you may be able to copy out your files using the DVD/Repair CD: Copy & Paste - in Windows Recovery Console

Then run factory recovery using disks you got with computer or made previously, or from its partition on HD. Or use a Win7 installaiton DVD to clean reinstall following these steps to get a Perfect Reinstall

Avoid tweaking Win7 as it is lean enough that it doesn´t tolerate much tweaking beyond normal system settings.

ok i resolved the issue, booted in safe mode and removed the theme pack, rebooted again and everything works fine now.

also the theme pack was in fact not infected with any malicious software, scanned the files and also my entire computer for any trojans or the like. but found nothing.

thanks for all the great help, even though the solution was something i could've probably thought of myself. ( wich i have infact, slapped myself in the face for. i might've been overthinking this).